Calcified tissues

The middle Ludlow beds, in the neighbourhood of Leintwarden, have, I believe, yielded the earliest vestiges of vertebrate life, a fragment of Pteraspis, or at least of a closely allied genus, having been discovered there some time ago. In the upper Ludlow rocks and Downton beds ichthyic remains become abundant, but in a sadly imperfect condition. In these localities, associated with Pterygotus, Platyschisma helicites, Lingula cornea, c while the Ludlow and Downton bone-beds are full of broken fragments of bones, spines, detached scales, and such like. The cornstones of Hereford have been found to contain similar remains. The Cephalaspid remains are for the most part readily recognised, all the rest are so broken up and fragmentary that, but for the light our Scottish Old Red Sandstone rocks have cast on these olden fishes, their nature and relations would have been comparatively unknown. None of our Scottish rocks affording fish remains are older than the lowermost beds of the Old Red Sandstone, and hence not so ancient as those of the above mentioned English localities, which, as Platyschisma helicites, Lingula cornea, and Beyrichia are also common to the Lesmahagow Upper Silurian or Passage Beds, appear to belong to a period immediately antecedent to that of the Scottish rocks affording our earliest known fish remains. Cephalaspis has long been known as a characteristic fossil of the Forfarshire Sandstones. Pteraspis was first discovered in Scotland by the Rev. Hugh Mitchell, in a quarry near Bridge of Allan, in

@article{doi101144transed13284,
    author = "Powrie, James",
    title = "On the earliest known vestiges of vertebrate life; being a description of the fish remains of the Old Red Sandstone rocks of Forfarshire",
    year = "1870",
    journal = "Transactions of the Edinburgh Geological Society",
    abstract = "The middle Ludlow beds, in the neighbourhood of Leintwarden, have, I believe, yielded the earliest vestiges of vertebrate life, a fragment of Pteraspis, or at least of a closely allied genus, having been discovered there some time ago. In the upper Ludlow rocks and Downton beds ichthyic remains become abundant, but in a sadly imperfect condition. In these localities, associated with Pterygotus, Platyschisma helicites, Lingula cornea, c while the Ludlow and Downton bone-beds are full of broken fragments of bones, spines, detached scales, and such like. The cornstones of Hereford have been found to contain similar remains. The Cephalaspid remains are for the most part readily recognised, all the rest are so broken up and fragmentary that, but for the light our Scottish Old Red Sandstone rocks have cast on these olden fishes, their nature and relations would have been comparatively unknown. None of our Scottish rocks affording fish remains are older than the lowermost beds of the Old Red Sandstone, and hence not so ancient as those of the above mentioned English localities, which, as Platyschisma helicites, Lingula cornea, and Beyrichia are also common to the Lesmahagow Upper Silurian or Passage Beds, appear to belong to a period immediately antecedent to that of the Scottish rocks affording our earliest known fish remains. Cephalaspis has long been known as a characteristic fossil of the Forfarshire Sandstones. Pteraspis was first discovered in Scotland by the Rev. Hugh Mitchell, in a quarry near Bridge of Allan, in",
    url = "https://doi.org/10.1144/transed.1.3.284",
    doi = "10.1144/transed.1.3.284",
    openalex = "W2322450156"
}

Summary Paley argued that because natural mechanisms often work like human mechanismsthey must have been made by a great designer; but this was an anthropomorphicfallacy which left the time element out of account. Darwin was able to show thatin many cases intergrades are known that connect even the most complex naturalmechanism with simpler antecedents; also his principle of the natural selectionof heritable variations seemed to provide a mechanism for the production ofmechanisms. However, the discovery of great numbers of what have been calledorthogenetic series has obscured the principle that the natural selection of smallheritable variations (mutations of the geneticists) I ˜nservesa nd integrates originallyindependent variables and tends to eliminate aberrant or “fortuitous” variationsand lethals that lie too far to one side of the curve. That there is indeed a subsidiarymechanism for the elimination of the vast majority of merely random variations issuggested by the discovery of “orbhers”, which preside over the course ofdevelopment and tend to keep it within prescribed limits (Spemann, 1927). It is not, however, the purpose of the present article to discuss the causes ofevolution but merely to formulate in general terms the ways in which organicdesigns of known history have originated and evolved, especially during theemergence and deployment of the vertebrates. An organic design is defined as acollocation of parts of an organic whole, varying in magnitude, emphasis or distancein space or time from the chosen point of origin or reference. As thus defined thechanges in many typical organic designs of known history may all be expressed asthe resultant of two co‐operative principles of individual development and phylogeneticevolution: the first may most briefly be called repetilion, the second emphasis. The principle of repetition has long been recognised in part under such names as “repetitive acceleration” (Cope), “metamerism” (Gegenbaur), “merism” (Bateson), “aristogenesis” (Osborn), while the principle of uneven development or emphasishas been called “differentiation” (Spencer), “alloiometry” (Osborn), “heterogony” (Pézard, J. S. Huqley), and so forth. For some years past the writer has beencalling the products of organic repetition polyisomnes and the general method ofrepetition, budding or reproduction polyisomerish; while for parts or regions that become unevenly developed, increased, decreased or fused with their neighboursthe term anisomeres is employed and the process itself is called anisornetism. Now one and now the other of these processes may predominate, but both are constantlyaltering organic designs to a greater or less degree. The term secondary polyisomerism is used to denote the important fact that when one polyisomere acquires a certaindetailed character its neighbours all along the line usually change in the samedirection. This, as it were, throws a screen of small details over the surface andimparts an often false appearance of simplicity, homogeneity and primitiveness towhat is in reality a very advanced stage of specialisation. When anisomeres areaffected by secondary polyisomerism the pattern tends toward dedifferentiation. After long periods of divergent evolution each of the diversified descendantgenera of a common stock will be found to be in possession of: (a) a mask of changedorganic designs relating especially to its particular mode of life, which is collectivelycalled its habitus, and (b) a smaller fund of unchanged organic designs or charactRtisticsinherited from the remote common stock, the totality of such charactersbeing called its anatomic heritage. Part of the habitus of a remote common ancestorafter a change of function becomes part of the heritage of its descendants, and thetwo correlative terms may be qualified so as to indicate such conditions as therelative phyletic ages of any particular habitus and heritage, or the relativesystematic values. Thus the swordfish‐like ordinal habitus of ichthyosaurs datesfrom Triassic times, but their reptilian clms heritage is of Permian age; the family habitus of the Macropodidae is kangaroo‐like, but their superfamiZy heritage isphalangeroid, By extension of the same principle we may speak of the habitusand heritage features of some particular division of an organic design, such as thejaws and dentition, the feet, the reproductive system and the like. Changes in habitus and heritage, if proceeding at slow rates or for relativelyshort periods, often convey the impression of orthogenesis, or undeviating evolution, but by combining the best established results of comparative anatomy and embryologywith the records of palaeontology over long periods of geologic time we discoverthe reality and frequence of the phenomenon of transfomtion. In reviewing the transformation of organic designs as seen in the deploymentof the vertebrates, the writer holds that his method has on the whole not been a priori, since the foregoing principles were established objectively after the actualhistory of the vertebrates had been illuminated by the largely independent laboursof a great number of geologists, palaeontologists and comparative anatomists, whofor the most part were always interested in solving concrete historical problemsrather than in considering the general principles of evolution. The principles ofrepetition and emphasis, of habitus and heritage, of undeviating evolution, transformationand the like, enable us to conceive the discrete facts of evolution ingeneral terms, but these concepts to be effectively applied must naturally besupplementary to discovery of the historical facts. With these provisos the writer has given a very brief review of the historicproblem of the origin of the vertebrates, rejecting the claims of various phyla, suchas the annelids, nemerteans, arthropods, etc., on different grounds and showingthat astonishing changes among certain echinoderms from an essentially quinqueradiateto a functionally bilateral symmetry warn us not to overlook thepossibility that the invertebrate ancestors of the vertebrates may not have beenbilaterally symmetrical, fusiform, free‐swimming types but possibly sessile bottomlivingforms with a strong dorso‐ventral asymmetry. The conclusions reached may be summarised as follows: Amphioxus is secondarily polyisomerous in many respects and anisomerous inothers, and may well be a degraded and highly specialised derivative of the oldestknown chordates, the ostracoderms. The contrasts are great between these earliest known chordates and any knowninvertebrates, with the posaible exception of the carpioid echinoderms. The most primitive of the ostracoderms appear to be among the Heterostraci, especially the poraspids. These are fusiform fishes with an armour of five platescovering the head and front part of the thorax. In the thelodonts and coelolepidsthe shield is represented by a great number of small tubercles or scales which havearisen by secondary polyisomerism from a once continuous head shield (Kiaer). The Heterostraci have paired nasal sacs, and according to Kiaer are related tothe ancestors of the jaw‐bearing fishes and higher vertebrates. From presentevidence this relationship may well be much closer than would be possible underthe older view that the heterostracous ostracoderms were a highly specialized side branch. The gnathostomous or jaw‐bearing vertebrates probably arose by transformationfrom agnathous creatures that bore no special resemblance to them except in thepossession of certain “basic patents”, especially the serial gill pouches. With regard to the origin of the modem Agnatha (lampreys and hagfishes), the superb material and intensive investigations of Stensio leave no doubt that thelampreys are derived from the cephalaspid ostracoderms, a result of great importancein the morphology of the central nervous system, since it confirms the conclusionsof neurologists that the arrangements of the cranial nerves and general brain patternsof the larval lamprey are on the whole much more primitive than those of theelasmobranchs. The investigations of Patten and Stensio on BothriOZepis and of Stensio on theArthrodira have proved that these long extinct placoderms represented earlyoffshoots from the base of the jaw‐bearing series of classes. They seem to thepresent writer also to be derived eventually from some agnathous but branchiateancestors who could not be very far from the most primitive of the heterostracousostracoderms. Heintz's admirable work an the evolution of the Arthrodira fromthe acanthaspids has also provided a clear example of the interaction of polyisomerisrnand anisomerism. The same principles are everywhere apparent in the recorded deployment ofthe higher vertebrates, as illustrated by the changes in the body form in the teleosts, or by the strange transformation of the mandible in the ancestry of the mammals. Thus one may gain a new perspective on the origin of that peculiarly variablesystem of organic designs that has called itself Homo sapiens, who after a prodigiousexpansion of his neopallium began to make organic designs for himself; then, wi

@article{doi101111j1469185x1936tb00909x,
    author = "Gregory, William K.",
    title = "THE TRANSFORMATION OF ORGANIC DESIGNS: A REVIEW OF THE ORIGIN AND DEPLOYMENT OF THE EARLIER VERTEBRATES",
    year = "1936",
    journal = "Biological reviews/Biological reviews of the Cambridge Philosophical Society",
    abstract = "Summary Paley argued that because natural mechanisms often work like human mechanismsthey must have been made by a great designer; but this was an anthropomorphicfallacy which left the time element out of account. Darwin was able to show thatin many cases intergrades are known that connect even the most complex naturalmechanism with simpler antecedents; also his principle of the natural selectionof heritable variations seemed to provide a mechanism for the production ofmechanisms. However, the discovery of great numbers of what have been calledorthogenetic series has obscured the principle that the natural selection of smallheritable variations (mutations of the geneticists) I ˜nservesa nd integrates originallyindependent variables and tends to eliminate aberrant or “fortuitous” variationsand lethals that lie too far to one side of the curve. That there is indeed a subsidiarymechanism for the elimination of the vast majority of merely random variations issuggested by the discovery of “orbhers”, which preside over the course ofdevelopment and tend to keep it within prescribed limits (Spemann, 1927). It is not, however, the purpose of the present article to discuss the causes ofevolution but merely to formulate in general terms the ways in which organicdesigns of known history have originated and evolved, especially during theemergence and deployment of the vertebrates. An organic design is defined as acollocation of parts of an organic whole, varying in magnitude, emphasis or distancein space or time from the chosen point of origin or reference. As thus defined thechanges in many typical organic designs of known history may all be expressed asthe resultant of two co‐operative principles of individual development and phylogeneticevolution: the first may most briefly be called repetilion, the second emphasis. The principle of repetition has long been recognised in part under such names as “repetitive acceleration” (Cope), “metamerism” (Gegenbaur), “merism” (Bateson), “aristogenesis” (Osborn), while the principle of uneven development or emphasishas been called “differentiation” (Spencer), “alloiometry” (Osborn), “heterogony” (Pézard, J. S. Huqley), and so forth. For some years past the writer has beencalling the products of organic repetition polyisomnes and the general method ofrepetition, budding or reproduction polyisomerish; while for parts or regions that become unevenly developed, increased, decreased or fused with their neighboursthe term anisomeres is employed and the process itself is called anisornetism. Now one and now the other of these processes may predominate, but both are constantlyaltering organic designs to a greater or less degree. The term secondary polyisomerism is used to denote the important fact that when one polyisomere acquires a certaindetailed character its neighbours all along the line usually change in the samedirection. This, as it were, throws a screen of small details over the surface andimparts an often false appearance of simplicity, homogeneity and primitiveness towhat is in reality a very advanced stage of specialisation. When anisomeres areaffected by secondary polyisomerism the pattern tends toward dedifferentiation. After long periods of divergent evolution each of the diversified descendantgenera of a common stock will be found to be in possession of: (a) a mask of changedorganic designs relating especially to its particular mode of life, which is collectivelycalled its habitus, and (b) a smaller fund of unchanged organic designs or charactRtisticsinherited from the remote common stock, the totality of such charactersbeing called its anatomic heritage. Part of the habitus of a remote common ancestorafter a change of function becomes part of the heritage of its descendants, and thetwo correlative terms may be qualified so as to indicate such conditions as therelative phyletic ages of any particular habitus and heritage, or the relativesystematic values. Thus the swordfish‐like ordinal habitus of ichthyosaurs datesfrom Triassic times, but their reptilian clms heritage is of Permian age; the family habitus of the Macropodidae is kangaroo‐like, but their superfamiZy heritage isphalangeroid, By extension of the same principle we may speak of the habitusand heritage features of some particular division of an organic design, such as thejaws and dentition, the feet, the reproductive system and the like. Changes in habitus and heritage, if proceeding at slow rates or for relativelyshort periods, often convey the impression of orthogenesis, or undeviating evolution, but by combining the best established results of comparative anatomy and embryologywith the records of palaeontology over long periods of geologic time we discoverthe reality and frequence of the phenomenon of transfomtion. In reviewing the transformation of organic designs as seen in the deploymentof the vertebrates, the writer holds that his method has on the whole not been a priori, since the foregoing principles were established objectively after the actualhistory of the vertebrates had been illuminated by the largely independent laboursof a great number of geologists, palaeontologists and comparative anatomists, whofor the most part were always interested in solving concrete historical problemsrather than in considering the general principles of evolution. The principles ofrepetition and emphasis, of habitus and heritage, of undeviating evolution, transformationand the like, enable us to conceive the discrete facts of evolution ingeneral terms, but these concepts to be effectively applied must naturally besupplementary to discovery of the historical facts. With these provisos the writer has given a very brief review of the historicproblem of the origin of the vertebrates, rejecting the claims of various phyla, suchas the annelids, nemerteans, arthropods, etc., on different grounds and showingthat astonishing changes among certain echinoderms from an essentially quinqueradiateto a functionally bilateral symmetry warn us not to overlook thepossibility that the invertebrate ancestors of the vertebrates may not have beenbilaterally symmetrical, fusiform, free‐swimming types but possibly sessile bottomlivingforms with a strong dorso‐ventral asymmetry. The conclusions reached may be summarised as follows: Amphioxus is secondarily polyisomerous in many respects and anisomerous inothers, and may well be a degraded and highly specialised derivative of the oldestknown chordates, the ostracoderms. The contrasts are great between these earliest known chordates and any knowninvertebrates, with the posaible exception of the carpioid echinoderms. The most primitive of the ostracoderms appear to be among the Heterostraci, especially the poraspids. These are fusiform fishes with an armour of five platescovering the head and front part of the thorax. In the thelodonts and coelolepidsthe shield is represented by a great number of small tubercles or scales which havearisen by secondary polyisomerism from a once continuous head shield (Kiaer). The Heterostraci have paired nasal sacs, and according to Kiaer are related tothe ancestors of the jaw‐bearing fishes and higher vertebrates. From presentevidence this relationship may well be much closer than would be possible underthe older view that the heterostracous ostracoderms were a highly specialized side branch. The gnathostomous or jaw‐bearing vertebrates probably arose by transformationfrom agnathous creatures that bore no special resemblance to them except in thepossession of certain “basic patents”, especially the serial gill pouches. With regard to the origin of the modem Agnatha (lampreys and hagfishes), the superb material and intensive investigations of Stensio leave no doubt that thelampreys are derived from the cephalaspid ostracoderms, a result of great importancein the morphology of the central nervous system, since it confirms the conclusionsof neurologists that the arrangements of the cranial nerves and general brain patternsof the larval lamprey are on the whole much more primitive than those of theelasmobranchs. The investigations of Patten and Stensio on BothriOZepis and of Stensio on theArthrodira have proved that these long extinct placoderms represented earlyoffshoots from the base of the jaw‐bearing series of classes. They seem to thepresent writer also to be derived eventually from some agnathous but branchiateancestors who could not be very far from the most primitive of the heterostracousostracoderms. Heintz's admirable work an the evolution of the Arthrodira fromthe acanthaspids has also provided a clear example of the interaction of polyisomerisrnand anisomerism. The same principles are everywhere apparent in the recorded deployment ofthe higher vertebrates, as illustrated by the changes in the body form in the teleosts, or by the strange transformation of the mandible in the ancestry of the mammals. Thus one may gain a new perspective on the origin of that peculiarly variablesystem of organic designs that has called itself Homo sapiens, who after a prodigiousexpansion of his neopallium began to make organic designs for himself; then, wi",
    url = "https://doi.org/10.1111/j.1469-185x.1936.tb00909.x",
    doi = "10.1111/j.1469-185x.1936.tb00909.x",
    openalex = "W2031207168"
}

@article{hoerman1964phosphorescence,
    author = "Hoerman, K.C. and Mancewicz, Sandra A.",
    title = "Phosphorescence of calcified tissues",
    year = "1964",
    journal = "Archives of Oral Biology",
    url = "https://doi.org/10.1016/0003-9969(64)90016-0",
    doi = "10.1016/0003-9969(64)90016-0",
    number = "5",
    pages = "517-IN3",
    volume = "9"
}

@book{crossref1966calcified,
    title = "Calcified Tissues 1965",
    year = "1966",
    url = "https://doi.org/10.1007/978-3-642-85841-3",
    doi = "10.1007/978-3-642-85841-3"
}

@article{nichols1967calcified,
    author = "Nichols, G.",
    title = "Calcified Tissues",
    year = "1967",
    journal = "Science",
    url = "https://doi.org/10.1126/science.157.3791.961",
    doi = "10.1126/science.157.3791.961",
    number = "3791",
    pages = "961-962",
    volume = "157"
}

@article{doi101007bf02058654,
    author = "Halstead, L. B.",
    title = "Calcified tissues in the earliest vertebrates",
    year = "1969",
    journal = "Calcified Tissue International",
    url = "https://doi.org/10.1007/bf02058654",
    doi = "10.1007/bf02058654",
    openalex = "W2093749224",
    references = "doi101017s0016756800082856, doi101017s0080456800035237, doi101038199046a0, doi10108002693445186812113227, doi101111j146363951940tb00339x, doi101111j146363951961tb00060x, doi105962bhltitle5752, openalexw2163397885, openalexw251296685, openalexw3003600068"
}

This paper deals with various vertebrates from the Verdalen Member of the Stjørdalen Formation of the Wood Bay Group, Vestspitsbergen, or layers presumably belonging to this member, including the thelodont scales Amaltheolepis winsnesi n.g., n.sp. (earlier known from a locality in Sørkapp Land), the heterostiid brachythoracid Herasmius granulatus n.g., n.sp. and the porolepiform crossopterygian Heimenia ensis n.g., n.sp., the latter with scales intermediate in some ways between those of Porolepis on the one hand, and the Holoptychiidae on the other. Amaltheolepis and Herasmius are not yet known to occur outside Vestspitsbergen; Heimenia is represented in a Devonian material from Anderson River, Northwestern Canada and perhaps also in the Placo‐derm Sandstone of Poland. A critical appraisal of the arthrodire faunas of the Wood Bay Group shows that most of the earlier recorded occurrences of Homostius and Heterostius in these layers pertain to euleptas‐pid brachythoracids, that the Heterostiidae and Homostiidae are also represented, but only in the Stjordalen Formation, and that the youngest member of the Euleptaspididae, occurring in the Stjordalen Formation, may be closely related to another euleptaspid in the Upper Emsian Heisdorf Beds of the Rhinish sequence (which occurs in association with Ohiolepis scales). The palaeontological evidence may indicate that the Wood Bay Group does not belong to the Lower Devonian in its entirety but includes Middle Devonian strata in its uppermost part.

@article{doi101111j150239311969tb01254x,
    author = "Ørvig, Tor",
    title = "VERTEBRATES FROM THE WOOD BAY GROUP AND THE POSITION OF THE EMSIAN‐EIFELIAN BOUNDARY IN THE DEVONIAN OF VESTSPITSBERGEN",
    year = "1969",
    journal = "Lethaia",
    abstract = "This paper deals with various vertebrates from the Verdalen Member of the Stjørdalen Formation of the Wood Bay Group, Vestspitsbergen, or layers presumably belonging to this member, including the thelodont scales Amaltheolepis winsnesi n.g., n.sp. (earlier known from a locality in Sørkapp Land), the heterostiid brachythoracid Herasmius granulatus n.g., n.sp. and the porolepiform crossopterygian Heimenia ensis n.g., n.sp., the latter with scales intermediate in some ways between those of Porolepis on the one hand, and the Holoptychiidae on the other. Amaltheolepis and Herasmius are not yet known to occur outside Vestspitsbergen; Heimenia is represented in a Devonian material from Anderson River, Northwestern Canada and perhaps also in the Placo‐derm Sandstone of Poland. A critical appraisal of the arthrodire faunas of the Wood Bay Group shows that most of the earlier recorded occurrences of Homostius and Heterostius in these layers pertain to euleptas‐pid brachythoracids, that the Heterostiidae and Homostiidae are also represented, but only in the Stjordalen Formation, and that the youngest member of the Euleptaspididae, occurring in the Stjordalen Formation, may be closely related to another euleptaspid in the Upper Emsian Heisdorf Beds of the Rhinish sequence (which occurs in association with Ohiolepis scales). The palaeontological evidence may indicate that the Wood Bay Group does not belong to the Lower Devonian in its entirety but includes Middle Devonian strata in its uppermost part.",
    url = "https://doi.org/10.1111/j.1502-3931.1969.tb01254.x",
    doi = "10.1111/j.1502-3931.1969.tb01254.x",
    openalex = "W2077948784",
    references = "doi101111j146363951961tb00060x"
}

@article{halstead1969calcified,
    author = "Halstead, L. Beverly",
    title = "Calcified tissues in the earliest vertebrates",
    year = "1969",
    journal = "Calcified Tissue Research",
    url = "https://doi.org/10.1007/bf02058654",
    doi = "10.1007/bf02058654",
    number = "1",
    pages = "107-124",
    volume = "3"
}

@article{nordin1969calcified,
    author = "Nordin, B. E. C. and Pautard, F. G. E.",
    title = "Calcified Tissues",
    year = "1969",
    journal = "Science",
    url = "https://doi.org/10.1126/science.164.3878.466",
    doi = "10.1126/science.164.3878.466",
    number = "3878",
    pages = "466-469",
    volume = "164"
}

@misc{tarlo1969calcified1,
    author = "Tarlo, L. B. H",
    title = "Calcified tissues in the earliest vertebrates",
    year = "1969",
    howpublished = "Calcified Tissue Research, v. 3, p. 107-124",
    note = "talkorigins\_source = {true}; raw\_reference = {Tarlo, L. B. H., 1969, Calcified tissues in the earliest vertebrates: Calcified Tissue Research, v. 3, p. 107-124.}"
}

@article{mccance1973calcified,
    author = "McCance, R. A.",
    title = "Calcified Tissues",
    year = "1973",
    journal = "BMJ",
    url = "https://doi.org/10.1136/bmj.2.5859.185",
    doi = "10.1136/bmj.2.5859.185",
    number = "5859",
    pages = "185.1-185",
    volume = "2"
}

@book{crossref1976calcified,
    title = "Calcified Tissues 1975",
    year = "1976",
    url = "https://doi.org/10.1007/978-3-662-29272-3",
    doi = "10.1007/978-3-662-29272-3"
}

@incollection{dirksen1977calcified,
    author = "Dirksen, Thomas R.",
    title = "Calcified Tissues",
    year = "1977",
    booktitle = "Lipid Metabolism in Mammals",
    url = "https://doi.org/10.1007/978-1-4684-0865-2\_8",
    doi = "10.1007/978-1-4684-0865-2\_8",
    pages = "237-292"
}

Abstract Fossil remains of primitive vertebrates, preserved in sandstone as natural moulds of the dermal armour, are described from the shallow-water marine Stairway Sandstone of the Amadeus Basin, Northern Territory, Australia. This is the first record of Ordovician vertebrates in the southern hemisphere. Two new genera and species, Arandaspis prionotolepis gen. et sp. nov. and Porophoraspis crenulata gen. et sp. nov., are described. Arandaspis is the most completely preserved of any known Ordovician vertebrate. It is the type genus of the new family Arandaspididae, and is referred to the new order Arandaspidiformes. The new Australian genera are provisionally interpreted as heterostracans, a group of agnathans not previously recorded from Australia. Deposition of the ostracoderm-bearing levels of the Stairway Sandstone is dated as earliest Middle Ordovician on the northern Australian shelly scale, or late Arenigian to early Llanvirnian on the British scale. The Australian forms thus approximate in age the Spitsbergen Anatolepis Bockelie & Fortey 1976, which is at present the oldest confirmed vertebrate fossil. They antedate the North American Harding Sandstone heterostracans Astraspis Walcott 1892 and Eriptychius Walcott 1892 by some 20 million years. Unlike the North American genera, the older forms from Australia and Spitsbergen are protected by a somewhat delicate non-tesserate shield, which invites a critical reassessment of current ideas on the course of evolution of early vertebrate armour and the date of its first appearance. The scale-like sculpture of the newly discovered forms also suggest a possible source of disjunct thelodont-like denticles recovered from Ordovician sediments. The wide geographical separation of the morphologically and temporally similar Australian and Spitsbergen genera, and the consistent association of Ordovician agnathans with marine invertebrates (both body fossils and trace fossils), uphold Denison's (1967, p. 141) conclusions concerning the habitat of early vertebrates: 'They lived in the sea. The regular association of their remains with sandstones and rarely with other sediments suggests that they lived on or above a sandy bottom. They preferred well-lighted, quiet waters at moderate depths in the sublittoral zone.'

@article{doi10108003115517708527770,
    author = "Ritchie, Alexander and Gilbert-Tomlinson, Joyce",
    title = "First Ordovician vertebrates from the Southern Hemisphere",
    year = "1977",
    journal = "Alcheringa An Australasian Journal of Palaeontology",
    abstract = "Abstract Fossil remains of primitive vertebrates, preserved in sandstone as natural moulds of the dermal armour, are described from the shallow-water marine Stairway Sandstone of the Amadeus Basin, Northern Territory, Australia. This is the first record of Ordovician vertebrates in the southern hemisphere. Two new genera and species, Arandaspis prionotolepis gen. et sp. nov. and Porophoraspis crenulata gen. et sp. nov., are described. Arandaspis is the most completely preserved of any known Ordovician vertebrate. It is the type genus of the new family Arandaspididae, and is referred to the new order Arandaspidiformes. The new Australian genera are provisionally interpreted as heterostracans, a group of agnathans not previously recorded from Australia. Deposition of the ostracoderm-bearing levels of the Stairway Sandstone is dated as earliest Middle Ordovician on the northern Australian shelly scale, or late Arenigian to early Llanvirnian on the British scale. The Australian forms thus approximate in age the Spitsbergen Anatolepis Bockelie \& Fortey 1976, which is at present the oldest confirmed vertebrate fossil. They antedate the North American Harding Sandstone heterostracans Astraspis Walcott 1892 and Eriptychius Walcott 1892 by some 20 million years. Unlike the North American genera, the older forms from Australia and Spitsbergen are protected by a somewhat delicate non-tesserate shield, which invites a critical reassessment of current ideas on the course of evolution of early vertebrate armour and the date of its first appearance. The scale-like sculpture of the newly discovered forms also suggest a possible source of disjunct thelodont-like denticles recovered from Ordovician sediments. The wide geographical separation of the morphologically and temporally similar Australian and Spitsbergen genera, and the consistent association of Ordovician agnathans with marine invertebrates (both body fossils and trace fossils), uphold Denison's (1967, p. 141) conclusions concerning the habitat of early vertebrates: 'They lived in the sea. The regular association of their remains with sandstones and rarely with other sediments suggests that they lived on or above a sandy bottom. They preferred well-lighted, quiet waters at moderate depths in the sublittoral zone.'",
    url = "https://doi.org/10.1080/03115517708527770",
    doi = "10.1080/03115517708527770",
    openalex = "W2058426945",
    references = "doi101111j1469185x1973tb01005x, doi101130gsab3153"
}

The objective of these experiments was to determine the embryonic origins of craniofacial and cervical voluntary muscles and associated connective tissues in the chick. To accomplish this, suspected primordia, including somitomeres 3-7, somites 1-7, and cephalic neural crest primordia have been transplanted from quail into chick embryos. Quail cells can be detected by the presence of a species-specific nuclear marker. The results are summarized as follows: (table; see text) These results indicate that muscles associated with branchial arch skeletal structures are derived from paraxial mesoderm, as are all other voluntary muscles in the vertebrate embryo. Thus, theories of vertebrate ontogeny and phylogeny based in part on proposed unique features of branchiomeric muscles must be critically reappraised. In addition, many of these cephalic muscles are composites of two separate primordia: the myogenic stem cells of mesodermal origin and the supporting and connective tissues derived from the neural crest or lateral plate mesoderm. Defining these embryonic origins is a necessary prerequisite to understanding how the mesenchymal primordia of cephalic muscles and connective tissues interact to form patterned, species-unique musculoskeletal systems.

@article{doi101002aja1001680302,
    author = "Noden, Drew M.",
    title = "The embryonic origins of avian cephalic and cervical muscles and associated connective tissues",
    year = "1983",
    journal = "American Journal of Anatomy",
    abstract = "The objective of these experiments was to determine the embryonic origins of craniofacial and cervical voluntary muscles and associated connective tissues in the chick. To accomplish this, suspected primordia, including somitomeres 3-7, somites 1-7, and cephalic neural crest primordia have been transplanted from quail into chick embryos. Quail cells can be detected by the presence of a species-specific nuclear marker. The results are summarized as follows: (table; see text) These results indicate that muscles associated with branchial arch skeletal structures are derived from paraxial mesoderm, as are all other voluntary muscles in the vertebrate embryo. Thus, theories of vertebrate ontogeny and phylogeny based in part on proposed unique features of branchiomeric muscles must be critically reappraised. In addition, many of these cephalic muscles are composites of two separate primordia: the myogenic stem cells of mesodermal origin and the supporting and connective tissues derived from the neural crest or lateral plate mesoderm. Defining these embryonic origins is a necessary prerequisite to understanding how the mesenchymal primordia of cephalic muscles and connective tissues interact to form patterned, species-unique musculoskeletal systems.",
    url = "https://doi.org/10.1002/aja.1001680302",
    doi = "10.1002/aja.1001680302",
    openalex = "W2098841171",
    references = "balfour1878a, doi101002aja1000920306, doi101002jmor1050880104, doi1010160002941683903329, doi1010160012160683903184, doi101016b9780120286089500065, doi101038142004a0, doi101086413055, doi101111j146363951940tb00339x, doi101126science2204594268, doi101242dev341125, doi1023072413058, doi105962bhltitle7847, doi105962bhltitle82144, openalexw197683541, openalexw251296685"
}

Most of the morphological and functional differences between vertebrates and other chordates occur in the head and are derived embryologically from muscularized hypomere, neural crest, and epidermal (neurogenic) placodes. In the head, the neural crest functions as mesoderm and forms connective, skeletal, and muscular tissue. Both the neural crest and the epidermal placodes form special sense organs and other neural structures. These structures may be homologous to portions of the epidermal nerve plexus of protochordates. The transition to vertebrates apparently was associated with a shift from a passive to an active mode of predation, so that many of the features occurring only in vertebrates became concentrated in the head.

@article{doi101126science2204594268,
    author = "Gans, Carl and Northcutt, R. Glenn",
    title = "Neural Crest and the Origin of Vertebrates: A New Head",
    year = "1983",
    journal = "Science",
    abstract = "Most of the morphological and functional differences between vertebrates and other chordates occur in the head and are derived embryologically from muscularized hypomere, neural crest, and epidermal (neurogenic) placodes. In the head, the neural crest functions as mesoderm and forms connective, skeletal, and muscular tissue. Both the neural crest and the epidermal placodes form special sense organs and other neural structures. These structures may be homologous to portions of the epidermal nerve plexus of protochordates. The transition to vertebrates apparently was associated with a shift from a passive to an active mode of predation, so that many of the features occurring only in vertebrates became concentrated in the head.",
    url = "https://doi.org/10.1126/science.220.4594.268",
    doi = "10.1126/science.220.4594.268",
    openalex = "W1997035797",
    references = "bone1961the, doi101002ar1091560204, doi101002cne901150105, doi101007bf02058654, doi1010160012160674902917, doi1010160012160675903188, doi1010160012160678902014, doi1010160014483579901647, doi101016b9780120286089500065, doi101086413055, doi101098rspb19680025, doi101098rspb19740058, doi101242dev341125, doi101242jcss27228551, halstead1969calcified"
}

@incollection{melsen1988calcified,
    author = "Melsen, F. and Mosekilde, L.",
    title = "Calcified Tissues: Cellular Dynamics",
    year = "1988",
    booktitle = "ILSI Human Nutrition Reviews",
    url = "https://doi.org/10.1007/978-1-4471-1437-6\_8",
    doi = "10.1007/978-1-4471-1437-6\_8",
    pages = "187-208"
}

This review deals with the following seven aspects of vertebrate skeletogenic and odontogenic tissues. 1. The evolutionary sequence in which the tissues appeared amongst the lower craniate taxa. 2. The topographic association between skeletal (cartilage, bone) and dental (dentine, cement, enamel) tissues in the oldest vertebrates of each major taxon. 3. The separate developmental origin of the exo- and endoskeletons. 4. The neural-crest origin of cranial skeletogenic and odontogenic tissues in extant vertebrates. 5. The neural-crest origin of trunk dermal skeletogenic and odontogenic tissues in extant vertebrates. 6. The developmental processes that control differentiation of skeletogenic and odontogenic tissues in extant vertebrates. 7. Maintenance of developmental interactions regulating skeletogenic/odontogenic differentiation across vertebrate taxa. We derive twelve postulates, eight relating to the earliest vertebrate skeletogenic and odontogenic tissues and four relating to the development of these tissues in extant vertebrates and extrapolate the developmental data back to the evolutionary origin of vertebrate skeletogenic and odontogenic tissues. The conclusions that we draw from this analysis are as follows. 8. The dermal exoskeleton of thelodonts, heterostracans and osteostracans consisted of dentine, attachment tissue (cement or bone), and bone. 9. Cartilage (unmineralized) can be inferred to have been present in heterostracans and osteostracans, and globular mineralized cartilage was present in Eriptychius, an early Middle Ordovician vertebrate unassigned to any established group, but assumed to be a stem agnathan. 10. Enamel and possibly also enameloid was present in some early agnathans of uncertain affinities. The majority of dentine tubercles were bare. 11. The contemporaneous appearance of cellular and acellular bone in heterostracans and osteostracans during the Ordovician provides no clue as to whether one is more primitive than the other. 12. We interpret aspidin as being developmentally related to the odontogenic attachment tissues, either closer to dentine or a form of cement, rather than as derived from bone. 13. Dentine is present in the stratigraphically oldest (Cambrian) assumed vertebrate fossils, at present some only included as Problematica, and is cladistically primitive, relative to bone. 14. The first vertebrate exoskeletal skeletogenic ability was expressed as denticles of dentine. 15. Dentine, the bone of attachment associated with dentine, the basal bone to which dermal denticles are fused and cartilage of the Ordovician agnathan dermal exoskeleton were all derived from the neural crest and not from mesoderm. Therefore the earliest vertebrate skeletogenic/odontogenic tissues were of neural-crest origin.(ABSTRACT TRUNCATED AT 400 WORDS)

@article{doi101111j1469185x1990tb01427x,
    author = "Smith, Moya Meredith and Hall, Brian K.",
    title = "DEVELOPMENT AND EVOLUTIONARY ORIGINS OF VERTEBRATE SKELETOGENIC AND ODONTOGENIC TISSUES",
    year = "1990",
    journal = "Biological reviews/Biological reviews of the Cambridge Philosophical Society",
    abstract = "This review deals with the following seven aspects of vertebrate skeletogenic and odontogenic tissues. 1. The evolutionary sequence in which the tissues appeared amongst the lower craniate taxa. 2. The topographic association between skeletal (cartilage, bone) and dental (dentine, cement, enamel) tissues in the oldest vertebrates of each major taxon. 3. The separate developmental origin of the exo- and endoskeletons. 4. The neural-crest origin of cranial skeletogenic and odontogenic tissues in extant vertebrates. 5. The neural-crest origin of trunk dermal skeletogenic and odontogenic tissues in extant vertebrates. 6. The developmental processes that control differentiation of skeletogenic and odontogenic tissues in extant vertebrates. 7. Maintenance of developmental interactions regulating skeletogenic/odontogenic differentiation across vertebrate taxa. We derive twelve postulates, eight relating to the earliest vertebrate skeletogenic and odontogenic tissues and four relating to the development of these tissues in extant vertebrates and extrapolate the developmental data back to the evolutionary origin of vertebrate skeletogenic and odontogenic tissues. The conclusions that we draw from this analysis are as follows. 8. The dermal exoskeleton of thelodonts, heterostracans and osteostracans consisted of dentine, attachment tissue (cement or bone), and bone. 9. Cartilage (unmineralized) can be inferred to have been present in heterostracans and osteostracans, and globular mineralized cartilage was present in Eriptychius, an early Middle Ordovician vertebrate unassigned to any established group, but assumed to be a stem agnathan. 10. Enamel and possibly also enameloid was present in some early agnathans of uncertain affinities. The majority of dentine tubercles were bare. 11. The contemporaneous appearance of cellular and acellular bone in heterostracans and osteostracans during the Ordovician provides no clue as to whether one is more primitive than the other. 12. We interpret aspidin as being developmentally related to the odontogenic attachment tissues, either closer to dentine or a form of cement, rather than as derived from bone. 13. Dentine is present in the stratigraphically oldest (Cambrian) assumed vertebrate fossils, at present some only included as Problematica, and is cladistically primitive, relative to bone. 14. The first vertebrate exoskeletal skeletogenic ability was expressed as denticles of dentine. 15. Dentine, the bone of attachment associated with dentine, the basal bone to which dermal denticles are fused and cartilage of the Ordovician agnathan dermal exoskeleton were all derived from the neural crest and not from mesoderm. Therefore the earliest vertebrate skeletogenic/odontogenic tissues were of neural-crest origin.(ABSTRACT TRUNCATED AT 400 WORDS)",
    url = "https://doi.org/10.1111/j.1469-185x.1990.tb01427.x",
    doi = "10.1111/j.1469-185x.1990.tb01427.x",
    openalex = "W2104126911",
    references = "doi10100797814615696887, doi101007bf02058654, doi1010160012160683903184, doi101017cbo9780511897948, doi101017s0016756800082856, doi101017s0080456800035237, doi101038282831a0, doi101038282833a0, doi101038scientificamerican0779122, doi10108002724634198110011886, doi10108002724634198410012014, doi101086413055, doi101093aesa323657, doi101111j109636421986tb00876x, doi101111j146363951940tb00339x, doi101111j146364091979tb00640x, doi101111j146364091980tb00660x, doi101111j1469185x1973tb01005x, doi101111j150239311983tb01993x, doi101111j150239311986tb00741x, doi101126science15737951472, doi101126science2204594268, doi101130gsab3153, doi1023072413259, doi1023072413454, doi1023072992444, doi105962bhltitle5752, doi105962bhltitle82144, halstead1969calcified, halstead1979agnathans, openalexw115975037, openalexw251296685, openalexw2591687711, openalexw2732375649, openalexw587905045"
}

From histological investigations into the microstructure of conodont elements, a number of tissue types characteristic of the phosphatic skeleton of vertebrates have been identified. These include cellular bone, two forms of hypermineralized enamel homologs, and globular calcified cartilage. The presence of cellular bone in conodont elements provides unequivocal evidence for their vertebrate affinities. Furthermore, the identification of vertebrate hard tissues in the oral elements of conodonts extends the earliest occurrence of vertebrate hard tissues back by around 40 million years, from the Middle Ordovician (475 million years ago) to the Late Cambrian (515 million years ago).

@article{doi101126science1598573,
    author = "Sansom, IJ and Smith, M. Paul and Armstrong, H. A. and Smith, Mm",
    title = "Presence of the Earliest Vertebrate Hard Tissue in Conodonts",
    year = "1992",
    journal = "Science",
    abstract = "From histological investigations into the microstructure of conodont elements, a number of tissue types characteristic of the phosphatic skeleton of vertebrates have been identified. These include cellular bone, two forms of hypermineralized enamel homologs, and globular calcified cartilage. The presence of cellular bone in conodont elements provides unequivocal evidence for their vertebrate affinities. Furthermore, the identification of vertebrate hard tissues in the oral elements of conodonts extends the earliest occurrence of vertebrate hard tissues back by around 40 million years, from the Middle Ordovician (475 million years ago) to the Late Cambrian (515 million years ago).",
    url = "https://doi.org/10.1126/science.1598573",
    doi = "10.1126/science.1598573",
    openalex = "W1991633942",
    references = "doi10108002724634198110011886, doi101111j146364091980tb00660x, doi101111j1469185x1990tb01427x, doi101111j150239311983tb01993x, doi101111j150239311986tb00741x, doi101111j150239311990tb01369x, doi1023071220820, doi1023071483846, doi105860choice266278, openalexw587905045"
}

The elastic moduli of calcified cartilage and subchondral bone tissues were measured experimentally with use of a three-point bending test. Specimens were obtained from a bovine patella and the distal end of a bovine femur, from two different animals. Fifteen specimens were tested as "pure" subchondral bone beams, and 15 were tested as composite calcified cartilage/subchondral bone beams. A least-squares optimization scheme was used to obtain modulus values from the composite beams. The elastic modulus for subchondral bone calculated from the "pure" subchondral bone beams was 2.3 +/- 1.5 GPa (3.9 +/- 1.5 GPa for specimens from the femur and 1.6 +/- 0.7 GPa for specimens from the patella). The composite beam optimization resulted in a modulus for subchondral bone of 5.7 +/- 1.9 GPa and a modulus for calcified cartilage of 0.32 +/- 0.25 GPa. The modulus for the calcified cartilage was more than an order of magnitude lower than the modulus of the underlying subchondral bone. This supports the idea that the zone of calcified cartilage forms a transitional zone of intermediate stiffness between the articular cartilage and the subchondral bone.

@article{doi101002jor1100120506,
    author = "Mente, Peter L. and Lewis, J. L.",
    title = "Elastic modulus of calcified cartilage is an order of magnitude less than that of subchondral bone",
    year = "1994",
    journal = "Journal of Orthopaedic Research®",
    abstract = {The elastic moduli of calcified cartilage and subchondral bone tissues were measured experimentally with use of a three-point bending test. Specimens were obtained from a bovine patella and the distal end of a bovine femur, from two different animals. Fifteen specimens were tested as "pure" subchondral bone beams, and 15 were tested as composite calcified cartilage/subchondral bone beams. A least-squares optimization scheme was used to obtain modulus values from the composite beams. The elastic modulus for subchondral bone calculated from the "pure" subchondral bone beams was 2.3 +/- 1.5 GPa (3.9 +/- 1.5 GPa for specimens from the femur and 1.6 +/- 0.7 GPa for specimens from the patella). The composite beam optimization resulted in a modulus for subchondral bone of 5.7 +/- 1.9 GPa and a modulus for calcified cartilage of 0.32 +/- 0.25 GPa. The modulus for the calcified cartilage was more than an order of magnitude lower than the modulus of the underlying subchondral bone. This supports the idea that the zone of calcified cartilage forms a transitional zone of intermediate stiffness between the articular cartilage and the subchondral bone.},
    url = "https://doi.org/10.1002/jor.1100120506",
    doi = "10.1002/jor.1100120506",
    openalex = "W2100821273"
}

Abstract This book presents our current knowledge of the early vertebrates, which were mainly fish, but included some land vertebrates, and lived about 470 to 250 million years ago. It centres on anatomical and phylogenetic questions, but includes information about fossil discovery and preparation, as well as the analysis of the characteristics from which their relationships may be reconstructed. It addresses critically both old and new problems in the evolution of certain anatomical structures and deals briefly with the animals' way of life, extinction, and former distribution. In addition, the author gives a potted history of the field of vertebrate palaeontology and the rise of cladistics, a major methodological revolution in comparative biology. The book is the first in theif field to use a cladistic approach. For each major vertebrate group, the reader will find a diagram of relationships, or cladogram, with a selection of characters at each node, and a cuccinct phylogenetic classification. The book is illustrated with numerous line drawings, culminating in a series of reconstructions of early vertebrates and their environment, which may have a more popular appeal.

@book{doi101093oso97801985404720010001,
    author = "Janvier, Philippe",
    title = "Early Vertebrates",
    year = "1996",
    abstract = "Abstract This book presents our current knowledge of the early vertebrates, which were mainly fish, but included some land vertebrates, and lived about 470 to 250 million years ago. It centres on anatomical and phylogenetic questions, but includes information about fossil discovery and preparation, as well as the analysis of the characteristics from which their relationships may be reconstructed. It addresses critically both old and new problems in the evolution of certain anatomical structures and deals briefly with the animals' way of life, extinction, and former distribution. In addition, the author gives a potted history of the field of vertebrate palaeontology and the rise of cladistics, a major methodological revolution in comparative biology. The book is the first in theif field to use a cladistic approach. For each major vertebrate group, the reader will find a diagram of relationships, or cladogram, with a selection of characters at each node, and a cuccinct phylogenetic classification. The book is illustrated with numerous line drawings, culminating in a series of reconstructions of early vertebrates and their environment, which may have a more popular appeal.",
    url = "https://doi.org/10.1093/oso/9780198540472.001.0001",
    doi = "10.1093/oso/9780198540472.001.0001",
    openalex = "W4388321741"
}

Osteichthyan and chondrichthyan fish present an astonishing diversity of skeletal and dental tissues that are often difficult to classify into the standard textbook categories of bone, cartilage, dentine and enamel. To address the question of how the tissues of the dermal skeleton evolved from the ancestral situation and gave rise to the diversity actually encountered, we review previous data on the development of a number of dermal skeletal elements (odontodes, teeth and dermal denticles, cranial dermal bones, postcranial dermal plates and scutes, elasmoid and ganoid scales, and fin rays). A comparison of developmental stages at the tissue level usually allows us to identify skeletogenic cell populations as either odontogenic or osteogenic on the basis of the place of formation of their dermal papillae and of the way of deposition of their tissues. Our studies support the evolutionary affinities (1) between odontodes, teeth and denticles, (2) between the ganoid scales of polypterids and the elasmoid scales of teleosts, and (3) to a lesser degree between the different bony elements. There is now ample evidence to ascertain that the tissues of the elasmoid scale are derived from dental and not from bony tissues. This review demonstrates the advantage that can be taken from developmental studies, at the tissue level, to infer evolutionary relationships within the dermal skeleton in chondrichthyans and osteichthyans.

@article{doi101017s1464793102006073,
    author = "Sire, Jean‐Yves and Huysseune, Ann",
    title = "Formation of dermal skeletal and dental tissues in fish: a comparative and evolutionary approach",
    year = "2003",
    journal = "Biological reviews/Biological reviews of the Cambridge Philosophical Society",
    abstract = "Osteichthyan and chondrichthyan fish present an astonishing diversity of skeletal and dental tissues that are often difficult to classify into the standard textbook categories of bone, cartilage, dentine and enamel. To address the question of how the tissues of the dermal skeleton evolved from the ancestral situation and gave rise to the diversity actually encountered, we review previous data on the development of a number of dermal skeletal elements (odontodes, teeth and dermal denticles, cranial dermal bones, postcranial dermal plates and scutes, elasmoid and ganoid scales, and fin rays). A comparison of developmental stages at the tissue level usually allows us to identify skeletogenic cell populations as either odontogenic or osteogenic on the basis of the place of formation of their dermal papillae and of the way of deposition of their tissues. Our studies support the evolutionary affinities (1) between odontodes, teeth and denticles, (2) between the ganoid scales of polypterids and the elasmoid scales of teleosts, and (3) to a lesser degree between the different bony elements. There is now ample evidence to ascertain that the tissues of the elasmoid scale are derived from dental and not from bony tissues. This review demonstrates the advantage that can be taken from developmental studies, at the tissue level, to infer evolutionary relationships within the dermal skeleton in chondrichthyans and osteichthyans.",
    url = "https://doi.org/10.1017/s1464793102006073",
    doi = "10.1017/s1464793102006073",
    openalex = "W2036850921",
    references = "doi101002jmor1051660303, doi10100797814615696887, doi101111j1469185x1999tb00045x, doi101111j160007221998tb02212x"
}

We studied articular calcified cartilage (ACC) and the immediately subchondral bone (SCB) in normal and osteoarthritic human femoral heads. Thick slices of human normal reference post mortem (PM) and osteoarthritic (OA) femoral heads (age 55-89 years) were embedded in PMMA, micromilled, carbon coated and studied using quantitative backscattered electron (qBSE) imaging to determine variations in degree of mineralization. With exact microanatomical location, nanoindentation was performed on the same block faces in representative superior (more highly loaded) and medial regions of the joint surface. Using a partial unloading method, elastic modulus as a function of indenter penetration depth was determined using a spherical tipped diamond indenter. A pointed indenter was used to determine the tissue hardness in selected locations. The relationship between mineralization and indentation modulus was more distinct in ACC than in SCB, the latter having a higher matrix concentration with variable collagen orientation. In OA, the bulk of the measurements were coincident with those in the PM samples, although there was a greater range in the levels of mineralization and modulus in ACC. In OA, extremely hypermineralized ACC was found in ACC proper, especially in superior regions, and translocated into SCB and hyaline cartilage. The very highly mineralized cartilage fragments may function as a hard grinding abrasive, accelerating wear rates whether attached to or fragmented from the eburnated surfaces of OA ACC. Highly mineralized regions would also alter loading patterns and thereby contribute to further destruction of the joint tissues.

@article{doi101046j14697580200300193x,
    author = "Ferguson, Virginia L. and Bushby, Andrew J. and Boyde, A.",
    title = "Nanomechanical properties and mineral concentration in articular calcified cartilage and subchondral bone",
    year = "2003",
    journal = "Journal of Anatomy",
    abstract = "We studied articular calcified cartilage (ACC) and the immediately subchondral bone (SCB) in normal and osteoarthritic human femoral heads. Thick slices of human normal reference post mortem (PM) and osteoarthritic (OA) femoral heads (age 55-89 years) were embedded in PMMA, micromilled, carbon coated and studied using quantitative backscattered electron (qBSE) imaging to determine variations in degree of mineralization. With exact microanatomical location, nanoindentation was performed on the same block faces in representative superior (more highly loaded) and medial regions of the joint surface. Using a partial unloading method, elastic modulus as a function of indenter penetration depth was determined using a spherical tipped diamond indenter. A pointed indenter was used to determine the tissue hardness in selected locations. The relationship between mineralization and indentation modulus was more distinct in ACC than in SCB, the latter having a higher matrix concentration with variable collagen orientation. In OA, the bulk of the measurements were coincident with those in the PM samples, although there was a greater range in the levels of mineralization and modulus in ACC. In OA, extremely hypermineralized ACC was found in ACC proper, especially in superior regions, and translocated into SCB and hyaline cartilage. The very highly mineralized cartilage fragments may function as a hard grinding abrasive, accelerating wear rates whether attached to or fragmented from the eburnated surfaces of OA ACC. Highly mineralized regions would also alter loading patterns and thereby contribute to further destruction of the joint tissues.",
    url = "https://doi.org/10.1046/j.1469-7580.2003.00193.x",
    doi = "10.1046/j.1469-7580.2003.00193.x",
    openalex = "W2100333150",
    references = "doi101002jor1100120506, doi101016s0003996902000067, doi101016s0021929099001116, doi101016s0142961297000732, doi101159000144288, doi101359jbmr1997124641, doi1015159781400853724, doi101557jmr19921564, doi101557jmr19930297, openalexw2408942088"
}

Abstract Patches of spherulitic calcified cartilage are described inside the paired fins of the osteostracan Escuminaspis laticeps from the Upper Devonian of Miguasha, Canada, thereby confirming Belles-Isles interpretation of these patches as evidence for paired fin endoskeleton. The distribution of these calcified cartilage patches suggests that the osteostracan paired fin endoskeleton was a single cartilaginous plate located in the lateral half of the fin, and was thus not made up of separate radials. This morphology resembles that of the endoskeletal disc of the embryonic and larval pectoral fin of piscine gnathostomes, prior to its decomposition into radials, and may mirror the general condition for the clade that includes osteostracans and gnathostomes.

@article{doi1016710272463420040240773ccitpf20co2,
    author = "Janvier, Philippe and Arsenault, Marius and Desbiens, Sylvain",
    title = "Calcified cartilage in the paired fins of the osteostracan Escuminaspis laticeps (Traquair 1880), from the Late Devonian of Miguasha (Québec, Canada), with a consideration of the early evolution of the pectoral fin endoskeleton in vertebrates",
    year = "2004",
    journal = "Journal of Vertebrate Paleontology",
    abstract = "Abstract Patches of spherulitic calcified cartilage are described inside the paired fins of the osteostracan Escuminaspis laticeps from the Upper Devonian of Miguasha, Canada, thereby confirming Belles-Isles interpretation of these patches as evidence for paired fin endoskeleton. The distribution of these calcified cartilage patches suggests that the osteostracan paired fin endoskeleton was a single cartilaginous plate located in the lateral half of the fin, and was thus not made up of separate radials. This morphology resembles that of the endoskeletal disc of the embryonic and larval pectoral fin of piscine gnathostomes, prior to its decomposition into radials, and may mirror the general condition for the clade that includes osteostracans and gnathostomes.",
    url = "https://doi.org/10.1671/0272-4634(2004)024[0773:ccitpf]2.0.co;2",
    doi = "10.1671/0272-4634(2004)024[0773:ccitpf]2.0.co;2",
    openalex = "W2174939881",
    references = "doi101111j109636421967tb01396x, doi101111j146363951961tb00060x"
}

The stratigraphically earliest and the most primitive examples of vertebrate skeletal mineralization belong to lineages that are entirely extinct. Therefore, palaeontology offers a singular opportunity to address the patterns and mechanisms of evolution in the vertebrate mineralized skeleton. We test the two leading hypotheses for the emergence of the four skeletal tissue types (bone, dentine, enamel, cartilage) that define the present state of skeletal tissue diversity in vertebrates. Although primitive vertebrate skeletons demonstrate a broad range of tissues that are difficult to classify, the first hypothesis maintains that the four skeletal tissue types emerged early in vertebrate phylogeny and that the full spectrum of vertebrate skeletal tissue diversity is explained by the traditional classification system. The opposing hypothesis suggests that the early evolution of the mineralized vertebrate skeleton was a time of plasticity and that the four tissue types did not emerge until later. On the basis of a considerable, and expanding, palaeontological dataset, we track the stratigraphic and phylogenetic histories of vertebrate skeletal tissues. With a cladistic perspective, we present findings that differ substantially from long-standing models of tissue evolution. Despite a greater diversity of skeletal tissues early in vertebrate phylogeny, our synthesis finds that bone, dentine, enamel and cartilage do appear to account for the full extent of this variation and do appear to be fundamentally distinct from their first inceptions, although why a higher diversity of tissue structural grades exists within these types early in vertebrate phylogeny is a question that remains to be addressed. Citing recent evidence that presents a correlation between duplication events in secretory calcium-binding phosphoproteins (SCPPs) and the structural complexity of mineralized tissues, we suggest that the high diversity of skeletal tissues early in vertebrate phylogeny may result from a low diversity of SCPPs and a corresponding lack of constraints on the mineralization of these tissues.

@article{doi101002jezb21090,
    author = "Donoghue, Philip C. J. and Sansom, Ivan J. and Downs, Jason P.",
    title = "Early evolution of vertebrate skeletal tissues and cellular interactions, and the canalization of skeletal development",
    year = "2006",
    journal = "Journal of Experimental Zoology Part B Molecular and Developmental Evolution",
    abstract = "The stratigraphically earliest and the most primitive examples of vertebrate skeletal mineralization belong to lineages that are entirely extinct. Therefore, palaeontology offers a singular opportunity to address the patterns and mechanisms of evolution in the vertebrate mineralized skeleton. We test the two leading hypotheses for the emergence of the four skeletal tissue types (bone, dentine, enamel, cartilage) that define the present state of skeletal tissue diversity in vertebrates. Although primitive vertebrate skeletons demonstrate a broad range of tissues that are difficult to classify, the first hypothesis maintains that the four skeletal tissue types emerged early in vertebrate phylogeny and that the full spectrum of vertebrate skeletal tissue diversity is explained by the traditional classification system. The opposing hypothesis suggests that the early evolution of the mineralized vertebrate skeleton was a time of plasticity and that the four tissue types did not emerge until later. On the basis of a considerable, and expanding, palaeontological dataset, we track the stratigraphic and phylogenetic histories of vertebrate skeletal tissues. With a cladistic perspective, we present findings that differ substantially from long-standing models of tissue evolution. Despite a greater diversity of skeletal tissues early in vertebrate phylogeny, our synthesis finds that bone, dentine, enamel and cartilage do appear to account for the full extent of this variation and do appear to be fundamentally distinct from their first inceptions, although why a higher diversity of tissue structural grades exists within these types early in vertebrate phylogeny is a question that remains to be addressed. Citing recent evidence that presents a correlation between duplication events in secretory calcium-binding phosphoproteins (SCPPs) and the structural complexity of mineralized tissues, we suggest that the high diversity of skeletal tissues early in vertebrate phylogeny may result from a low diversity of SCPPs and a corresponding lack of constraints on the mineralization of these tissues.",
    url = "https://doi.org/10.1002/jez.b.21090",
    doi = "10.1002/jez.b.21090",
    openalex = "W2027753758",
    references = "doi10100797814899175155, doi101007bf02058654, doi101017s0006323199005472, doi101017s0263593300002595, doi101038199046a0, doi10103831927, doi101038361129a0, doi101073pnas0638023100, doi10108002724634198410012014, doi101093oso97801985404720010001, doi101098rspb19990617, doi101111j1469185x1990tb01427x, doi101111j1469185x1999tb00045x, doi101111j160007221998tb02212x, doi101371journalpbio0030314, doi105860choice341531, doi105962bhltitle118830, halstead1969calcified, openalexw251296685, openalexw3003600068"
}

The genetic basis of the development and variation of adult form of vertebrates is not well understood. To address this problem, we performed a mutant screen to identify genes essential for the formation of adult skeletal structures of the zebrafish. Here, we describe the phenotypic and molecular characterization of a set of mutants showing loss of adult structures of the dermal skeleton, such as the rays of the fins and the scales, as well as the pharyngeal teeth. The mutations represent adult-viable, loss of function alleles in the ectodysplasin (eda) and ectodysplasin receptor (edar) genes. These genes are frequently mutated in the human hereditary disease hypohidrotic ectodermal dysplasia (HED; OMIM 224900, 305100) that affects the development of integumentary appendages such as hair and teeth. We find mutations in zebrafish edar that affect similar residues as mutated in human cases of HED and show similar phenotypic consequences. eda and edar are not required for early zebrafish development, but are rather specific for the development of adult skeletal and dental structures. We find that the defects of the fins and scales are due to the role of Eda signaling in organizing epidermal cells into discrete signaling centers of the scale epidermal placode and fin fold. Our genetic analysis demonstrates dose-sensitive and organ-specific response to alteration in levels of Eda signaling. In addition, we show substantial buffering of the effect of loss of edar function in different genetic backgrounds, suggesting canalization of this developmental system. We uncover a previously unknown role of Eda signaling in teleosts and show conservation of the developmental mechanisms involved in the formation and variation of both integumentary appendages and limbs. Lastly, our findings point to the utility of adult genetic screens in the zebrafish in identifying essential developmental processes involved in human disease and in morphological evolution.

@article{doi101371journalpgen1000206,
    author = "Harris, Matthew P. and Rohner, Nicolas and Schwarz, Heinz and Perathoner, Simon and Konstantinidis, Peter and Nüsslein‐Volhard, Christiane",
    title = "Zebrafish eda and edar Mutants Reveal Conserved and Ancestral Roles of Ectodysplasin Signaling in Vertebrates",
    year = "2008",
    journal = "PLoS Genetics",
    abstract = "The genetic basis of the development and variation of adult form of vertebrates is not well understood. To address this problem, we performed a mutant screen to identify genes essential for the formation of adult skeletal structures of the zebrafish. Here, we describe the phenotypic and molecular characterization of a set of mutants showing loss of adult structures of the dermal skeleton, such as the rays of the fins and the scales, as well as the pharyngeal teeth. The mutations represent adult-viable, loss of function alleles in the ectodysplasin (eda) and ectodysplasin receptor (edar) genes. These genes are frequently mutated in the human hereditary disease hypohidrotic ectodermal dysplasia (HED; OMIM 224900, 305100) that affects the development of integumentary appendages such as hair and teeth. We find mutations in zebrafish edar that affect similar residues as mutated in human cases of HED and show similar phenotypic consequences. eda and edar are not required for early zebrafish development, but are rather specific for the development of adult skeletal and dental structures. We find that the defects of the fins and scales are due to the role of Eda signaling in organizing epidermal cells into discrete signaling centers of the scale epidermal placode and fin fold. Our genetic analysis demonstrates dose-sensitive and organ-specific response to alteration in levels of Eda signaling. In addition, we show substantial buffering of the effect of loss of edar function in different genetic backgrounds, suggesting canalization of this developmental system. We uncover a previously unknown role of Eda signaling in teleosts and show conservation of the developmental mechanisms involved in the formation and variation of both integumentary appendages and limbs. Lastly, our findings point to the utility of adult genetic screens in the zebrafish in identifying essential developmental processes involved in human disease and in morphological evolution.",
    url = "https://doi.org/10.1371/journal.pgen.1000206",
    doi = "10.1371/journal.pgen.1000206",
    openalex = "W2086253706",
    references = "doi101002jemt10217"
}

Undoubted fossil lampreys are recorded since the Late Devonian (358 Ma), and probable fossil hagfishes since the Late Carboniferous (300 Ma), but molecular clock data suggest a much earlier divergence times for the two groups. In the early 20(th) century, hagfishes and lampreys were generally thought to have diverged much later from unknown ancestral cyclostomes, in turn derived through 'degeneracy' from some Paleozoic armored jawless vertebrates, or 'ostracoderms.' However, current vertebrate phylogenies suggest that most, if not all, 'ostracoderms' are in fact jawless stem gnathostomes, which retain certain features that were once regarded as unique to the cyclostomes, such as gill pouches or lack of horizontal semicircular canal. The dorsal, median, nasohypophysial complex of osteostracans has been regarded as identical and homologous to that of lampreys, but recent investigation (notably on the galeaspid braincase) now suggests that this resemblance is in fact a convergence. The anatomy and physiology of lampreys and hagfishes are so different that it is difficult to reconstruct an ancestral morphotype of the cyclostomes, assuming that they are a clade, and there is no clear evidence of any fossil taxon that is neither a fossil hagfish nor a fossil lamprey, but would be more closely related to the cyclostomes than to the gnathostomes. A possible exception is the Silurian-Devonian euphaneropids (or 'naked anaspids').

@article{doi102108zsj251045,
    author = "Janvier, Philippe",
    title = "Early Jawless Vertebrates and Cyclostome Origins",
    year = "2008",
    journal = "ZOOLOGICAL SCIENCE",
    abstract = "Undoubted fossil lampreys are recorded since the Late Devonian (358 Ma), and probable fossil hagfishes since the Late Carboniferous (300 Ma), but molecular clock data suggest a much earlier divergence times for the two groups. In the early 20(th) century, hagfishes and lampreys were generally thought to have diverged much later from unknown ancestral cyclostomes, in turn derived through 'degeneracy' from some Paleozoic armored jawless vertebrates, or 'ostracoderms.' However, current vertebrate phylogenies suggest that most, if not all, 'ostracoderms' are in fact jawless stem gnathostomes, which retain certain features that were once regarded as unique to the cyclostomes, such as gill pouches or lack of horizontal semicircular canal. The dorsal, median, nasohypophysial complex of osteostracans has been regarded as identical and homologous to that of lampreys, but recent investigation (notably on the galeaspid braincase) now suggests that this resemblance is in fact a convergence. The anatomy and physiology of lampreys and hagfishes are so different that it is difficult to reconstruct an ancestral morphotype of the cyclostomes, assuming that they are a clade, and there is no clear evidence of any fossil taxon that is neither a fossil hagfish nor a fossil lamprey, but would be more closely related to the cyclostomes than to the gnathostomes. A possible exception is the Silurian-Devonian euphaneropids (or 'naked anaspids').",
    url = "https://doi.org/10.2108/zsj.25.1045",
    doi = "10.2108/zsj.25.1045",
    openalex = "W2129690732",
    references = "doi10100797894011583432, doi101017s0016756800082856, doi101111j146364091974tb00816x"
}

We used light microscopy and scanning electron microscopy to compile a complete histological description of the dermal skeleton of the antiarch placoderm, Bothriolepis canadensis. Placodermi is most often cited as the sister group of crown group Gnathostomata, but some recent authors propose that placoderms instead represent a paraphyly of forms leading to the crown. In either phylogenetic scenario, comparative analysis of placoderm and gnathostome histological data allows us to address the primitive condition of both the gnathostome skeleton and the jawed vertebrate skeleton. The results of this work support the interpretation that the external skeleton of Bothriolepis canadensis is comprised exclusively of cellular dermal bone tissue. The unique stratification of the antiarch thoracic skeleton that has led to controversial interpretations in the past is explained by the nature of the articulations between adjacent elements. Skeletal features long thought to be gnathostome innovations are instead discovered to arise along the gnathostome stem. These innovations include secondary osteons, the systematic reconstruction of the skeleton in response to growth, and unfused, overlapping joints that enable marginal growth while maximizing the area of the articulation surface. The extensive evidence for spheritic mineralization agrees with a model of the skeleton as one capable of a high growth rate and active remodeling. Dermal skeletal development in both placoderms and osteichthyans is primarily skeletogenetic with only a minor odontogenetic contribution in some taxa. This demonstrates the problem inherent with assuming a broad application for those hypotheses of dermal skeletal evolution that are based on a chondrichthyan model. Our results highlight the importance of anatomical and ontogenetic context in the interpretation of fossil tissues.

@article{doi101002jmor10765,
    author = "Downs, Jason P. and Donoghue, Philip C. J.",
    title = "Skeletal histology of Bothriolepis canadensis (Placodermi, Antiarchi) and evolution of the skeleton at the origin of jawed vertebrates",
    year = "2009",
    journal = "Journal of Morphology",
    abstract = "We used light microscopy and scanning electron microscopy to compile a complete histological description of the dermal skeleton of the antiarch placoderm, Bothriolepis canadensis. Placodermi is most often cited as the sister group of crown group Gnathostomata, but some recent authors propose that placoderms instead represent a paraphyly of forms leading to the crown. In either phylogenetic scenario, comparative analysis of placoderm and gnathostome histological data allows us to address the primitive condition of both the gnathostome skeleton and the jawed vertebrate skeleton. The results of this work support the interpretation that the external skeleton of Bothriolepis canadensis is comprised exclusively of cellular dermal bone tissue. The unique stratification of the antiarch thoracic skeleton that has led to controversial interpretations in the past is explained by the nature of the articulations between adjacent elements. Skeletal features long thought to be gnathostome innovations are instead discovered to arise along the gnathostome stem. These innovations include secondary osteons, the systematic reconstruction of the skeleton in response to growth, and unfused, overlapping joints that enable marginal growth while maximizing the area of the articulation surface. The extensive evidence for spheritic mineralization agrees with a model of the skeleton as one capable of a high growth rate and active remodeling. Dermal skeletal development in both placoderms and osteichthyans is primarily skeletogenetic with only a minor odontogenetic contribution in some taxa. This demonstrates the problem inherent with assuming a broad application for those hypotheses of dermal skeletal evolution that are based on a chondrichthyan model. Our results highlight the importance of anatomical and ontogenetic context in the interpretation of fossil tissues.",
    url = "https://doi.org/10.1002/jmor.10765",
    doi = "10.1002/jmor.10765",
    openalex = "W2102014557",
    references = "doi101111j146363951961tb00060x"
}

The uneven distribution of species richness is a fundamental and unexplained pattern of vertebrate biodiversity. Although species richness in groups like mammals, birds, or teleost fishes is often attributed to accelerated cladogenesis, we lack a quantitative conceptual framework for identifying and comparing the exceptional changes of tempo in vertebrate evolutionary history. We develop MEDUSA, a stepwise approach based upon the Akaike information criterion for detecting multiple shifts in birth and death rates on an incompletely resolved phylogeny. We apply MEDUSA incompletely to a diversity tree summarizing both evolutionary relationships and species richness of 44 major clades of jawed vertebrates. We identify 9 major changes in the tempo of gnathostome diversification; the most significant of these lies at the base of a clade that includes most of the coral-reef associated fishes as well as cichlids and perches. Rate increases also underlie several well recognized tetrapod radiations, including most modern birds, lizards and snakes, ostariophysan fishes, and most eutherian mammals. In addition, we find that large sections of the vertebrate tree exhibit nearly equal rates of origination and extinction, providing some of the first evidence from molecular data for the importance of faunal turnover in shaping biodiversity. Together, these results reveal living vertebrate biodiversity to be the product of volatile turnover punctuated by 6 accelerations responsible for >85% of all species as well as 3 slowdowns that have produced "living fossils." In addition, by revealing the timing of the exceptional pulses of vertebrate diversification as well as the clades that experience them, our diversity tree provides a framework for evaluating particular causal hypotheses of vertebrate radiations.

@article{doi101073pnas0811087106,
    author = "Alfaro, Michael E. and Santini, Francesco and Brock, Chad D. and Alamillo, Hugo and Dornburg, Alex and Rabosky, Daniel L. and Carnevale, Giorgio and Harmon, Luke J.",
    title = "Nine exceptional radiations plus high turnover explain species diversity in jawed vertebrates",
    year = "2009",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = {The uneven distribution of species richness is a fundamental and unexplained pattern of vertebrate biodiversity. Although species richness in groups like mammals, birds, or teleost fishes is often attributed to accelerated cladogenesis, we lack a quantitative conceptual framework for identifying and comparing the exceptional changes of tempo in vertebrate evolutionary history. We develop MEDUSA, a stepwise approach based upon the Akaike information criterion for detecting multiple shifts in birth and death rates on an incompletely resolved phylogeny. We apply MEDUSA incompletely to a diversity tree summarizing both evolutionary relationships and species richness of 44 major clades of jawed vertebrates. We identify 9 major changes in the tempo of gnathostome diversification; the most significant of these lies at the base of a clade that includes most of the coral-reef associated fishes as well as cichlids and perches. Rate increases also underlie several well recognized tetrapod radiations, including most modern birds, lizards and snakes, ostariophysan fishes, and most eutherian mammals. In addition, we find that large sections of the vertebrate tree exhibit nearly equal rates of origination and extinction, providing some of the first evidence from molecular data for the importance of faunal turnover in shaping biodiversity. Together, these results reveal living vertebrate biodiversity to be the product of volatile turnover punctuated by 6 accelerations responsible for >85\% of all species as well as 3 slowdowns that have produced "living fossils." In addition, by revealing the timing of the exceptional pulses of vertebrate diversification as well as the clades that experience them, our diversity tree provides a framework for evaluating particular causal hypotheses of vertebrate radiations.},
    url = "https://doi.org/10.1073/pnas.0811087106",
    doi = "10.1073/pnas.0811087106",
    openalex = "W2151413057",
    references = "doi10108002724634199810011114, doi101086627905, doi10560219780801882210, openalexw628087051"
}

Most non-tetrapod vertebrates develop mineralized extra-oral elements within the integument. Known collectively as the integumentary skeleton, these elements represent the structurally diverse skin-bound contribution to the dermal skeleton. In this review we begin by summarizing what is known about the histological diversity of the four main groups of integumentary skeletal tissues: hypermineralized (capping) tissues; dentine; plywood-like tissues; and bone. For most modern taxa, the integumentary skeleton has undergone widespread reduction and modification often rendering the homology and relationships of these elements confused and uncertain. Fundamentally, however, all integumentary skeletal elements are derived (alone or in combination) from only two types of cell condensations: odontogenic and osteogenic condensations. We review the origin and diversification of the integumentary skeleton in aquatic non-tetrapods (including stem gnathostomes), focusing on tissues derived from odontogenic (hypermineralized tissues, dentines and elasmodine) and osteogenic (bone tissues) cell condensations. The novelty of our new scenario of integumentary skeletal evolution resides in the demonstration that elasmodine, the main component of elasmoid scales, is odontogenic in origin. Based on available data we propose that elasmodine is a form of lamellar dentine. Given its widespread distribution in non-tetrapod lineages we further propose that elasmodine is a very ancient tissue in vertebrates and predict that it will be found in ancestral rhombic scales and cosmoid scales.

@article{doi101111j14697580200901046x,
    author = "Sire, Jean‐Yves and Donoghue, Philip C. J. and Vickaryous, Matthews K.",
    title = "Origin and evolution of the integumentary skeleton in non‐tetrapod vertebrates",
    year = "2009",
    journal = "Journal of Anatomy",
    abstract = "Most non-tetrapod vertebrates develop mineralized extra-oral elements within the integument. Known collectively as the integumentary skeleton, these elements represent the structurally diverse skin-bound contribution to the dermal skeleton. In this review we begin by summarizing what is known about the histological diversity of the four main groups of integumentary skeletal tissues: hypermineralized (capping) tissues; dentine; plywood-like tissues; and bone. For most modern taxa, the integumentary skeleton has undergone widespread reduction and modification often rendering the homology and relationships of these elements confused and uncertain. Fundamentally, however, all integumentary skeletal elements are derived (alone or in combination) from only two types of cell condensations: odontogenic and osteogenic condensations. We review the origin and diversification of the integumentary skeleton in aquatic non-tetrapods (including stem gnathostomes), focusing on tissues derived from odontogenic (hypermineralized tissues, dentines and elasmodine) and osteogenic (bone tissues) cell condensations. The novelty of our new scenario of integumentary skeletal evolution resides in the demonstration that elasmodine, the main component of elasmoid scales, is odontogenic in origin. Based on available data we propose that elasmodine is a form of lamellar dentine. Given its widespread distribution in non-tetrapod lineages we further propose that elasmodine is a very ancient tissue in vertebrates and predict that it will be found in ancestral rhombic scales and cosmoid scales.",
    url = "https://doi.org/10.1111/j.1469-7580.2009.01046.x",
    doi = "10.1111/j.1469-7580.2009.01046.x",
    openalex = "W2157790551",
    references = "doi101002jemt10217, doi101002jezb21090, doi101002sici15211878200002222138aidbies530co24, doi10100797814615696887, doi101007bf02058654, doi101017cbo9780511897948, doi101017s0006323199005472, doi101017s0263593300002595, doi101029sc005p0175, doi101038199046a0, doi101038nature01264, doi10108010635150590950326, doi101093molbevmsl150, doi101093oso97801985404720010001, doi101111j146363951961tb00060x, doi101111j146364091980tb00660x, doi101111j1469185x1973tb01005x, doi101111j1469185x1991tb01138x, doi101111j1469185x1999tb00045x, doi101111j14697580200901066x, doi101126science1598573, doi1023071292217, doi105860choice326223, doi105962bhltitle118830, halstead1969calcified, openalexw1490966724, openalexw1587561751, openalexw251296685, openalexw3003600068, openalexw598239287"
}

Placoderms, the most diverse group of Devonian fishes, were globally distributed in all habitable freshwater and marine environments, like teleost fishes in the modern fauna. Their known evolutionary history (Early Silurian–Late Devonian) spanned at least 70 million years. Known diversity (335 genera) will increase when diverse assemblages from new areas are described. Placoderms first occur in the Early Silurian of China, but their diversity remained low until their main evolutionary radiation in the Early Devonian, after which they became the dominant vertebrates of Devonian seas. Most current placoderm data are derived from the second half of the group's evolutionary history, and recent claims that they form a paraphyletic group are based on highly derived Late Devonian forms; 16 shared derived characters are proposed here to support placoderm monophyly. Interrelationships of seven placoderm orders are unresolved because Silurian forms from China are still poorly known. The relationship of placoderms to the two major extant groups of jawed fishes—osteichthyans (bony fishes) and chondrichthyans (cartilaginous sharks, rays, and chimaeras)—remains uncertain, but the detailed preservation of placoderm internal braincase structures provides insights into the ancestral gnathostome (jawed vertebrate) condition. Placoderms provide the most complex morphological and biogeographic data set for the Middle Paleozoic; marked discrepancies in stratigraphic occurrence between different continental regions indicate strongly endemic faunas that were probably constrained by marine barriers until changes in paleogeography permitted range enlargement into new areas. Placoderm distributions in time and space indicate major faunal interchange between Gondwana and Laurussia near the Frasnian-Famennian boundary; closure of the Devonian equatorial ocean is a possible explanation.

@article{doi101146annurevearth040809152507,
    author = "Young, Gavin C.",
    title = "Placoderms (Armored Fish): Dominant Vertebrates of the Devonian Period",
    year = "2010",
    journal = "Annual Review of Earth and Planetary Sciences",
    abstract = "Placoderms, the most diverse group of Devonian fishes, were globally distributed in all habitable freshwater and marine environments, like teleost fishes in the modern fauna. Their known evolutionary history (Early Silurian–Late Devonian) spanned at least 70 million years. Known diversity (335 genera) will increase when diverse assemblages from new areas are described. Placoderms first occur in the Early Silurian of China, but their diversity remained low until their main evolutionary radiation in the Early Devonian, after which they became the dominant vertebrates of Devonian seas. Most current placoderm data are derived from the second half of the group's evolutionary history, and recent claims that they form a paraphyletic group are based on highly derived Late Devonian forms; 16 shared derived characters are proposed here to support placoderm monophyly. Interrelationships of seven placoderm orders are unresolved because Silurian forms from China are still poorly known. The relationship of placoderms to the two major extant groups of jawed fishes—osteichthyans (bony fishes) and chondrichthyans (cartilaginous sharks, rays, and chimaeras)—remains uncertain, but the detailed preservation of placoderm internal braincase structures provides insights into the ancestral gnathostome (jawed vertebrate) condition. Placoderms provide the most complex morphological and biogeographic data set for the Middle Paleozoic; marked discrepancies in stratigraphic occurrence between different continental regions indicate strongly endemic faunas that were probably constrained by marine barriers until changes in paleogeography permitted range enlargement into new areas. Placoderm distributions in time and space indicate major faunal interchange between Gondwana and Laurussia near the Frasnian-Famennian boundary; closure of the Devonian equatorial ocean is a possible explanation.",
    url = "https://doi.org/10.1146/annurev-earth-040809-152507",
    doi = "10.1146/annurev-earth-040809-152507",
    openalex = "W2169739871",
    references = "doi101002gj1072, doi101098rsbl20070545, doi101111j109636421986tb00876x, doi105962bhltitle5752"
}

OBJECTIVE: Alkaptonuria is a genetic disorder of tyrosine metabolism, resulting in elevated circulating concentrations of homogentisic acid. Homogentisic acid is deposited as a polymer, termed ochronotic pigment, in collagenous tissues, especially cartilages of weight-bearing joints, leading to a severe osteoarthropathy. We undertook this study to investigate the initiation and progression of ochronosis from the earliest detection of pigment through complete joint failure. METHODS: Nine joint samples with varying severities of ochronosis were obtained from alkaptonuria patients undergoing surgery and compared to joint samples obtained from osteoarthritis (OA) patients. Samples were analyzed by light and fluorescence microscopy, 3-dimensional scanning electron microscopy (SEM), and the quantitative backscattered electron mode of SEM. Cartilage samples were mechanically tested by compression to determine Young's modulus of pigmented, nonpigmented, and OA cartilage samples. RESULTS: In alkaptonuria samples with the least advanced ochronosis, pigment was observed intracellularly and in the territorial matrix of individual chondrocytes at the boundary of the subchondral bone and calcified cartilage. In more advanced ochronosis, pigmentation was widespread throughout the hyaline cartilage in either granular composition or as blanket pigmentation in which there is complete and homogenous pigmentation of cartilage matrix. Once hyaline cartilage was extensively pigmented, there was aggressive osteoclastic resorption of the subchondral plate. Pigmented cartilage became impacted on less highly mineralized trabeculae and embedded in the marrow space. Pigmented cartilage samples were much stiffer than nonpigmented or OA cartilage as revealed by a significant difference in Young's modulus. CONCLUSION: Using alkaptonuria cartilage specimens with a wide spectrum of pigmentation, we have characterized the progression of ochronosis. Intact cartilage appears to be resistant to pigmentation but becomes susceptible following focal changes in calcified cartilage. Ochronosis spreads throughout the cartilage, altering the mechanical properties. In advanced ochronosis, there is aggressive resorption of the underlying calcified cartilage leading to an extraordinary phenotype in which there is complete loss of the subchondral plate. These findings should contribute to better understanding of cartilage-subchondral interactions in arthropathies.

@article{doi101002art30606,
    author = "Taylor, A M and Boyde, A and Wilson, P J M and Jarvis, J C and Davidson, J S and Hunt, J A and Ranganath, L R and Gallagher, J A",
    title = "The role of calcified cartilage and subchondral bone in the initiation and progression of ochronotic arthropathy in alkaptonuria.",
    year = "2011",
    journal = "Arthritis and rheumatism",
    abstract = "OBJECTIVE: Alkaptonuria is a genetic disorder of tyrosine metabolism, resulting in elevated circulating concentrations of homogentisic acid. Homogentisic acid is deposited as a polymer, termed ochronotic pigment, in collagenous tissues, especially cartilages of weight-bearing joints, leading to a severe osteoarthropathy. We undertook this study to investigate the initiation and progression of ochronosis from the earliest detection of pigment through complete joint failure. METHODS: Nine joint samples with varying severities of ochronosis were obtained from alkaptonuria patients undergoing surgery and compared to joint samples obtained from osteoarthritis (OA) patients. Samples were analyzed by light and fluorescence microscopy, 3-dimensional scanning electron microscopy (SEM), and the quantitative backscattered electron mode of SEM. Cartilage samples were mechanically tested by compression to determine Young's modulus of pigmented, nonpigmented, and OA cartilage samples. RESULTS: In alkaptonuria samples with the least advanced ochronosis, pigment was observed intracellularly and in the territorial matrix of individual chondrocytes at the boundary of the subchondral bone and calcified cartilage. In more advanced ochronosis, pigmentation was widespread throughout the hyaline cartilage in either granular composition or as blanket pigmentation in which there is complete and homogenous pigmentation of cartilage matrix. Once hyaline cartilage was extensively pigmented, there was aggressive osteoclastic resorption of the subchondral plate. Pigmented cartilage became impacted on less highly mineralized trabeculae and embedded in the marrow space. Pigmented cartilage samples were much stiffer than nonpigmented or OA cartilage as revealed by a significant difference in Young's modulus. CONCLUSION: Using alkaptonuria cartilage specimens with a wide spectrum of pigmentation, we have characterized the progression of ochronosis. Intact cartilage appears to be resistant to pigmentation but becomes susceptible following focal changes in calcified cartilage. Ochronosis spreads throughout the cartilage, altering the mechanical properties. In advanced ochronosis, there is aggressive resorption of the underlying calcified cartilage leading to an extraordinary phenotype in which there is complete loss of the subchondral plate. These findings should contribute to better understanding of cartilage-subchondral interactions in arthropathies.",
    url = "https://pubmed.ncbi.nlm.nih.gov/22127706/",
    doi = "10.1002/art.30606",
    openalex = "W2064682336",
    pmid = "22127706",
    references = "doi101002art20124, doi1010160002934363900895, doi101016jbone200508007, doi101016s0021925818705607, doi101038ng099619, doi101046j14697580200300193x, doi101056nejmoa021736, doi101093rheumatologykeg327, doi101136ard2008098764, doi102106jbjsh01408"
}

The origin of jaws remains largely an enigma that is best addressed by studying fossil and living jawless vertebrates. Conodonts were eel-shaped jawless animals, whose vertebrate affinity is still disputed. The geometrical analysis of exceptional three-dimensionally preserved clusters of oro-pharyngeal elements of the Early Triassic Novispathodus, imaged using propagation phase-contrast X-ray synchrotron microtomography, suggests the presence of a pulley-shaped lingual cartilage similar to that of extant cyclostomes within the feeding apparatus of euconodonts ("true" conodonts). This would lend strong support to their interpretation as vertebrates and demonstrates that the presence of such cartilage is a plesiomorphic condition of crown vertebrates.

@article{doi101073pnas1101754108,
    author = "Goudemand, Nicolas and Orchard, Michael J. and Urdy, Séverine and Bucher, Hugo and Tafforeau, Paul",
    title = "Synchrotron-aided reconstruction of the conodont feeding apparatus and implications for the mouth of the first vertebrates",
    year = "2011",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = {The origin of jaws remains largely an enigma that is best addressed by studying fossil and living jawless vertebrates. Conodonts were eel-shaped jawless animals, whose vertebrate affinity is still disputed. The geometrical analysis of exceptional three-dimensionally preserved clusters of oro-pharyngeal elements of the Early Triassic Novispathodus, imaged using propagation phase-contrast X-ray synchrotron microtomography, suggests the presence of a pulley-shaped lingual cartilage similar to that of extant cyclostomes within the feeding apparatus of euconodonts ("true" conodonts). This would lend strong support to their interpretation as vertebrates and demonstrates that the presence of such cartilage is a plesiomorphic condition of crown vertebrates.},
    url = "https://doi.org/10.1073/pnas.1101754108",
    doi = "10.1073/pnas.1101754108",
    openalex = "W2166651471",
    references = "doi101111j150239311990tb01369x, doi1016660022336020000740113oaanic20co2, doi105252g2010n4a1"
}

OBJECTIVE: The objective of this study is to develop a method for selective detection of the calcific (hydroxyapatite) component in human aortic smooth muscle cells in vitro and in calcified cardiovascular tissues ex vivo. This method uses a novel optical molecular imaging contrast dye, Cy-HABP-19, to target calcified cells and tissues. METHODS: A peptide that mimics the binding affinity of osteocalcin was used to label hydroxyapatite in vitro and ex vivo. Morphological changes in vascular smooth muscle cells were evaluated at an early stage of the mineralization process induced by extrinsic stimuli, osteogenic factors and a magnetic suspension cell culture. Hydroxyapatite components were detected in monolayers of these cells in the presence of osteogenic factors and a magnetic suspension environment. RESULTS: Atherosclerotic plaque contains multiple components including lipidic, fibrotic, thrombotic, and calcific materials. Using optical imaging and the Cy-HABP-19 molecular imaging probe, we demonstrated that hydroxyapatite components could be selectively distinguished from various calcium salts in human aortic smooth muscle cells in vitro and in calcified cardiovascular tissues, carotid endarterectomy samples and aortic valves, ex vivo. CONCLUSION: Hydroxyapatite deposits in cardiovascular tissues were selectively detected in the early stage of the calcification process using our Cy-HABP-19 probe. This new probe makes it possible to study the earliest events associated with vascular hydroxyapatite deposition at the cellular and molecular levels. This target-selective molecular imaging probe approach holds high potential for revealing early pathophysiological changes, leading to progression, regression, or stabilization of cardiovascular diseases.

@article{doi101016jatherosclerosis201207023,
    author = "Lee, Jae Sam and Morrisett, Joel D and Tung, Ching-Hsuan",
    title = "Detection of hydroxyapatite in calcified cardiovascular tissues.",
    year = "2012",
    journal = "Atherosclerosis",
    abstract = "OBJECTIVE: The objective of this study is to develop a method for selective detection of the calcific (hydroxyapatite) component in human aortic smooth muscle cells in vitro and in calcified cardiovascular tissues ex vivo. This method uses a novel optical molecular imaging contrast dye, Cy-HABP-19, to target calcified cells and tissues. METHODS: A peptide that mimics the binding affinity of osteocalcin was used to label hydroxyapatite in vitro and ex vivo. Morphological changes in vascular smooth muscle cells were evaluated at an early stage of the mineralization process induced by extrinsic stimuli, osteogenic factors and a magnetic suspension cell culture. Hydroxyapatite components were detected in monolayers of these cells in the presence of osteogenic factors and a magnetic suspension environment. RESULTS: Atherosclerotic plaque contains multiple components including lipidic, fibrotic, thrombotic, and calcific materials. Using optical imaging and the Cy-HABP-19 molecular imaging probe, we demonstrated that hydroxyapatite components could be selectively distinguished from various calcium salts in human aortic smooth muscle cells in vitro and in calcified cardiovascular tissues, carotid endarterectomy samples and aortic valves, ex vivo. CONCLUSION: Hydroxyapatite deposits in cardiovascular tissues were selectively detected in the early stage of the calcification process using our Cy-HABP-19 probe. This new probe makes it possible to study the earliest events associated with vascular hydroxyapatite deposition at the cellular and molecular levels. This target-selective molecular imaging probe approach holds high potential for revealing early pathophysiological changes, leading to progression, regression, or stabilization of cardiovascular diseases.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC3459140/",
    doi = "10.1016/j.atherosclerosis.2012.07.023",
    openalex = "W1971017079",
    pmcid = "PMC3459140",
    pmid = "22877867",
    references = "doi101016jcell200705047, doi101016jcell201006003, doi10103835025203, doi101038382448a0, doi101038386078a0, doi101159000350089, doi10116101atv2051262, doi10116101res00002493795553521, doi10116101res877e10, doi101161hh2401101070"
}

@article{doi101038nature11555,
    author = "Rücklin, Martin and Donoghue, Philip C. J. and Johanson, Zerina and Trinajstic, Kate and Marone, Federica and Stampanoni, Marco",
    title = "Development of teeth and jaws in the earliest jawed vertebrates",
    year = "2012",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature11555",
    doi = "10.1038/nature11555",
    openalex = "W1995047221",
    references = "doi101002bies200900151, doi101111j109636421986tb00876x, doi101111j146364091980tb00660x"
}

Abstract The oldest known Palaeozoic vertebrate record currently is Early Cambrian in age. The first taxa with mineralized exoskeletons are at least Ordovician in age, followed by a sporadic fossil record with Talimaa’s Gap of c. 3 myr in the Rhuddanian (earliest Silurian). Ordovician and Silurian vertebrate faunas are dominated by ‘agnathans’. Early Palaeozoic vertebrates occupied a wide range of environments: nearshore marine to restricted marine in the Ordovician, and on the marine epicontinental shelves of the Silurian. Silurian vertebrates are useful biostratigraphical indicators, as well as good markers of palaeocontinental margins. Two main palaeobiogeographical units are renamed for the Ordovician: a Gondwana Realm and a Laurentia–Siberia–Baltica Realm. Vertebrate fossil localities are more numerous in the Silurian; therefore a series of palaeobiogeographical provinces and realms are defined on Laurentia, Baltica, Avalonia, Siberia, South China and East Gondwana. More discoveries of Silurian vertebrate-bearing localities should certainly help to define additional provinces, in particular along the northern margins of Gondwana and in SE Asia.

@article{doi101144m3828,
    author = "Žigaitė, Živilė and Blieck, Alain",
    title = "Chapter 28 Palaeobiogeography of Early Palaeozoic vertebrates",
    year = "2013",
    journal = "Geological Society London Memoirs",
    abstract = "Abstract The oldest known Palaeozoic vertebrate record currently is Early Cambrian in age. The first taxa with mineralized exoskeletons are at least Ordovician in age, followed by a sporadic fossil record with Talimaa’s Gap of c. 3 myr in the Rhuddanian (earliest Silurian). Ordovician and Silurian vertebrate faunas are dominated by ‘agnathans’. Early Palaeozoic vertebrates occupied a wide range of environments: nearshore marine to restricted marine in the Ordovician, and on the marine epicontinental shelves of the Silurian. Silurian vertebrates are useful biostratigraphical indicators, as well as good markers of palaeocontinental margins. Two main palaeobiogeographical units are renamed for the Ordovician: a Gondwana Realm and a Laurentia–Siberia–Baltica Realm. Vertebrate fossil localities are more numerous in the Silurian; therefore a series of palaeobiogeographical provinces and realms are defined on Laurentia, Baltica, Avalonia, Siberia, South China and East Gondwana. More discoveries of Silurian vertebrate-bearing localities should certainly help to define additional provinces, in particular along the northern margins of Gondwana and in SE Asia.",
    url = "https://doi.org/10.1144/m38.28",
    doi = "10.1144/m38.28",
    openalex = "W2116590018",
    references = "doi101017s0016756800082856, openalexw1485830652, openalexw2208603329"
}

Connective tissues such as tendons or ligaments attach to bone across a multitissue interface with spatial gradients in composition, structure, and mechanical properties. These gradients minimize stress concentrations and mediate load transfer between the soft and hard tissues. Given the high incidence of tendon and ligament injuries and the lack of integrative solutions for their repair, interface regeneration remains a significant clinical challenge. This review begins with a description of the developmental processes and the resultant structure-function relationships that translate into the functional grading necessary for stress transfer between soft tissue and bone. It then discusses the interface healing response, with a focus on the influence of mechanical loading and the role of cell-cell interactions. The review continues with a description of current efforts in interface tissue engineering, highlighting key strategies for the regeneration of the soft tissue-to-bone interface, and concludes with a summary of challenges and future directions.

@article{doi101146annurevbioeng071910124656,
    author = "Lu, Helen H. and Thomopoulos, Stavros",
    title = "Functional Attachment of Soft Tissues to Bone: Development, Healing, and Tissue Engineering",
    year = "2013",
    journal = "Annual Review of Biomedical Engineering",
    abstract = "Connective tissues such as tendons or ligaments attach to bone across a multitissue interface with spatial gradients in composition, structure, and mechanical properties. These gradients minimize stress concentrations and mediate load transfer between the soft and hard tissues. Given the high incidence of tendon and ligament injuries and the lack of integrative solutions for their repair, interface regeneration remains a significant clinical challenge. This review begins with a description of the developmental processes and the resultant structure-function relationships that translate into the functional grading necessary for stress transfer between soft tissue and bone. It then discusses the interface healing response, with a focus on the influence of mechanical loading and the role of cell-cell interactions. The review continues with a description of current efforts in interface tissue engineering, highlighting key strategies for the regeneration of the soft tissue-to-bone interface, and concludes with a summary of challenges and future directions.",
    url = "https://doi.org/10.1146/annurev-bioeng-071910-124656",
    doi = "10.1146/annurev-bioeng-071910-124656",
    openalex = "W2156622891",
    references = "doi101046j14697580200300193x"
}

Chondrichthyan-like scales with simple, single-odontode crowns, reminiscent of those of euselachians, have been reported from Silurian strata in a number of previous studies. These specimens comprise the genera Elegestolepis (from Siberia, Mongolia, and Tuva) and Kannathalepis (from the Canadian Arctic) and have been considered to exhibit contrasting patterns of ontogenetic development. A study of elegestolepid microremains from the Chargat Formation of Mongolia (Llandovery–lower Wenlock) and the Baital Formation of Tuva (Wenlock–Ludlow) has been undertaken using scanning electron microscopy and micro-computed tomography to examine scale canal system and hard tissue structure. These investigations revealed scales at different stages of development, whose morphogenesis is characterized by growth (elongation) of the crown odontode and formation of neck canals. This ontogenetic pattern (Elegestolepis-type morphogenesis) is also recognized in Kannathalepis and the Lower Devonian species Ellesmereia schultzei and forms the basis for the unification of these taxa into a new chondrichthyan order Elegestolepidida, ordo nov. Similarities in crown vascularization (branching pulp, single neck canal) shared by Elegestolepis, Ellesmereia, and Deltalepis, gen. nov. (D. magna, sp. nov., and D. parva, sp. nov., erected herein for Mongolian specimens), require the erection of the family Elegestolepididae, fam. nov., that is distinguished from the monogeneric Kannathalepididae (non-branching pulp, multiple neck canals). Elegestolepid scales exhibit characteristics (neck canal formation and lack of enamel and basal bone osteons) consistent with those of the chondrichthyan dermal skeleton. This establishes Elegestolepidida as the stratigraphically oldest chondrichthyan taxon to develop monodontode scales, which, in contrast to the ‘placoid’ scales of euselachians, are growing structures.http://zoobank.org/urn:lsid:zoobank.org:pub:46F95C47-6926-4F3DB96D-9890527BA8DECitation for this article: Andreev, P. S., M. I. Coates, V. Karatajūtė-Talimaa, R. M. Shelton, P. R. Cooper, and I. J. Sansom. 2016. Elegestolepis and its kin, the earliest monodontode chondrichthyans. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1245664.

@article{doi1010800272463420171245664,
    author = "Andreev, Plamen S. and Coates, Michael I. and Karatajūtė‐Talimaa, Valentina and Shelton, Richard M. and Cooper, Paul R. and Sansom, Ivan J.",
    title = "Elegestolepis and its kin, the earliest monodontode chondrichthyans",
    year = "2016",
    journal = "Journal of Vertebrate Paleontology",
    abstract = "Chondrichthyan-like scales with simple, single-odontode crowns, reminiscent of those of euselachians, have been reported from Silurian strata in a number of previous studies. These specimens comprise the genera Elegestolepis (from Siberia, Mongolia, and Tuva) and Kannathalepis (from the Canadian Arctic) and have been considered to exhibit contrasting patterns of ontogenetic development. A study of elegestolepid microremains from the Chargat Formation of Mongolia (Llandovery–lower Wenlock) and the Baital Formation of Tuva (Wenlock–Ludlow) has been undertaken using scanning electron microscopy and micro-computed tomography to examine scale canal system and hard tissue structure. These investigations revealed scales at different stages of development, whose morphogenesis is characterized by growth (elongation) of the crown odontode and formation of neck canals. This ontogenetic pattern (Elegestolepis-type morphogenesis) is also recognized in Kannathalepis and the Lower Devonian species Ellesmereia schultzei and forms the basis for the unification of these taxa into a new chondrichthyan order Elegestolepidida, ordo nov. Similarities in crown vascularization (branching pulp, single neck canal) shared by Elegestolepis, Ellesmereia, and Deltalepis, gen. nov. (D. magna, sp. nov., and D. parva, sp. nov., erected herein for Mongolian specimens), require the erection of the family Elegestolepididae, fam. nov., that is distinguished from the monogeneric Kannathalepididae (non-branching pulp, multiple neck canals). Elegestolepid scales exhibit characteristics (neck canal formation and lack of enamel and basal bone osteons) consistent with those of the chondrichthyan dermal skeleton. This establishes Elegestolepidida as the stratigraphically oldest chondrichthyan taxon to develop monodontode scales, which, in contrast to the ‘placoid’ scales of euselachians, are growing structures.http://zoobank.org/urn:lsid:zoobank.org:pub:46F95C47-6926-4F3DB96D-9890527BA8DECitation for this article: Andreev, P. S., M. I. Coates, V. Karatajūtė-Talimaa, R. M. Shelton, P. R. Cooper, and I. J. Sansom. 2016. Elegestolepis and its kin, the earliest monodontode chondrichthyans. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1245664.",
    url = "https://doi.org/10.1080/02724634.2017.1245664",
    doi = "10.1080/02724634.2017.1245664",
    openalex = "W2550674372",
    references = "doi101111j146363951961tb00060x"
}

BACKGROUND: Calcification of the yellow ligament sometimes compresses the spinal cord and can induce myelopathy. Usually, the calcification does not induce acute neck pain. We report a case of a patient with acute neck pain caused by calcium pyrophosphate dihydrate in a calcified cervical yellow ligament. CASE PRESENTATION: A 70-year-old Japanese woman presented with acute neck pain. She had a moderately high fever (37.5 °C), and her neck pain was so severe that she could not move her neck in any direction. Computed tomography showed a high-density area between the C5 and C6 laminae suspicious for calcification of the yellow ligament. Magnetic resonance imaging showed intermediate-signal intensity on T1-weighted imaging and high-signal intensity on T2-weighted imaging surrounding a low-signal region on both T1- and T2-weighted imaging with cord compression. There was a turbid, yellow fluid collection in the yellow ligament at the time of operation. Histologically, calcium pyrophosphate dihydrate crystals were found in the fluid, and she was diagnosed as having a pseudogout attack of the yellow ligament. CONCLUSIONS: Pseudogout attack of the cervical yellow ligament is rare, but this clinical entity should be added to the differential diagnosis of acute neck pain, especially when calcification of the yellow ligament exists.

@article{doi101186s1325601609281,
    author = "Kobayashi, Takashi and Miyakoshi, Naohisa and Abe, Toshiki and Abe, Eiji and Kikuchi, Kazuma and Noguchi, Hideaki and Konno, Norikazu and Shimada, Yoichi",
    title = "Acute neck pain caused by pseudogout attack of calcified cervical yellow ligament: a case report",
    year = "2016",
    journal = "Journal of Medical Case Reports",
    abstract = "BACKGROUND: Calcification of the yellow ligament sometimes compresses the spinal cord and can induce myelopathy. Usually, the calcification does not induce acute neck pain. We report a case of a patient with acute neck pain caused by calcium pyrophosphate dihydrate in a calcified cervical yellow ligament. CASE PRESENTATION: A 70-year-old Japanese woman presented with acute neck pain. She had a moderately high fever (37.5 °C), and her neck pain was so severe that she could not move her neck in any direction. Computed tomography showed a high-density area between the C5 and C6 laminae suspicious for calcification of the yellow ligament. Magnetic resonance imaging showed intermediate-signal intensity on T1-weighted imaging and high-signal intensity on T2-weighted imaging surrounding a low-signal region on both T1- and T2-weighted imaging with cord compression. There was a turbid, yellow fluid collection in the yellow ligament at the time of operation. Histologically, calcium pyrophosphate dihydrate crystals were found in the fluid, and she was diagnosed as having a pseudogout attack of the yellow ligament. CONCLUSIONS: Pseudogout attack of the cervical yellow ligament is rare, but this clinical entity should be added to the differential diagnosis of acute neck pain, especially when calcification of the yellow ligament exists.",
    url = "https://doi.org/10.1186/s13256-016-0928-1",
    doi = "10.1186/s13256-016-0928-1",
    openalex = "W2401263449"
}

INTRODUCTION: Calcification of ligamentum flavum (CLF) is an important cause of spinal stenosis and spinal cord compression. CLF does not usually induce immediate quadriparesis. Here we describe a rare case of immediate quadriparesis due to a large calcified mass containing liquids in the ligamentum flavum, which was easily confused with gout crystals. PATIENT CONCERNS: A 74-year-old Asian male felt progressive bilateral arm and leg weakness. On the fourth day, acute quadriparesis occurred. DIAGNOSIS: Coronal and sagittal computerized tomography (CT) and magnetic resonance imaging (MRI) showed a large circular mass in the left posterior part of the cervical 3/4 spinal canal, protruding into the canal, and occupying one-half of the spinal canal. INTERVENTIONS: Emergency laminectomy was performed at C3/4 level. The huge cyst was excised and 1 ml of white viscous liquid flowed out. OUTCOMES: After operation, CT and MRI showed a full laminectomy of C3/4 and complete decompression of the cervical spinal cord. Hematoxylin-eosin (HE) staining showed that large amounts of calcium was deposited around cystic tissues. Five-year follow-up after laminectomy showed good recovery. CONCLUSION: This case of immediate quadriparesis, caused by a large calcified mass containing fluid, is very rare. It should be at the earliest stage of calcification. Laminectomy is an effective treatment. This calcification was deceptive and was easily confused with gout crystals. It can help to understand the exact pathophysiology of CLF.

@article{doi101097md0000000000017456,
    author = "Cao, Yafei and Li, Heng and Liu, Weidong and Yu, Weiji and Gao, Kun",
    title = "Five years of follow-up of immediate quadriparesis caused by a large calcified mass in the ligamentum flavum: A case report.",
    year = "2019",
    journal = "Medicine",
    abstract = "INTRODUCTION: Calcification of ligamentum flavum (CLF) is an important cause of spinal stenosis and spinal cord compression. CLF does not usually induce immediate quadriparesis. Here we describe a rare case of immediate quadriparesis due to a large calcified mass containing liquids in the ligamentum flavum, which was easily confused with gout crystals. PATIENT CONCERNS: A 74-year-old Asian male felt progressive bilateral arm and leg weakness. On the fourth day, acute quadriparesis occurred. DIAGNOSIS: Coronal and sagittal computerized tomography (CT) and magnetic resonance imaging (MRI) showed a large circular mass in the left posterior part of the cervical 3/4 spinal canal, protruding into the canal, and occupying one-half of the spinal canal. INTERVENTIONS: Emergency laminectomy was performed at C3/4 level. The huge cyst was excised and 1 ml of white viscous liquid flowed out. OUTCOMES: After operation, CT and MRI showed a full laminectomy of C3/4 and complete decompression of the cervical spinal cord. Hematoxylin-eosin (HE) staining showed that large amounts of calcium was deposited around cystic tissues. Five-year follow-up after laminectomy showed good recovery. CONCLUSION: This case of immediate quadriparesis, caused by a large calcified mass containing fluid, is very rare. It should be at the earliest stage of calcification. Laminectomy is an effective treatment. This calcification was deceptive and was easily confused with gout crystals. It can help to understand the exact pathophysiology of CLF.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC6824699/",
    doi = "10.1097/MD.0000000000017456",
    openalex = "W2981350735",
    pmcid = "PMC6824699",
    pmid = "31651848",
    references = "doi101016jnec201709016, doi101055s00341366979, doi101097md0000000000004468, doi101148radiology17831994435, doi101186s1325601507871, doi101186s1325601609281, doi101259bjrcr20170049, doi103171jns19835930531, doi104184asj20148189, openalexw1458278700"
}

The Siluro-Devonian adaptive radiation of jawed vertebrates, which underpins almost all living vertebrate biodiversity, is characterized by the evolutionary innovation of the lower jaw. Multiple lines of evidence have suggested that the jaw evolved from a rostral gill arch, but when the jaw took on a feeding function remains unclear. We quantified the variety of form in the earliest jaws in the fossil record from which we generated a theoretical morphospace that we then tested for functional optimality. By drawing comparisons with the real jaw data and reconstructed jaw morphologies from phylogenetically inferred ancestors, our results show that the earliest jaw shapes were optimized for fast closure and stress resistance, inferring a predatory feeding function. Jaw shapes became less optimal for these functions during the later radiation of jawed vertebrates. Thus, the evolution of jaw morphology has continually explored previously unoccupied morphospace and accumulated disparity through time, laying the foundation for diverse feeding strategies and the success of jawed vertebrates.

@article{doi101126sciadvabl3644,
    author = "Deakin, William J. and Anderson, Philip S. L. and den Boer, Wendy and Smith, Thomas J. and Hill, Jennifer J. and Rücklin, Martin and Donoghue, Philip C. J. and Rayfield, Emily J.",
    title = "Increasing morphological disparity and decreasing optimality for jaw speed and strength during the radiation of jawed vertebrates",
    year = "2022",
    journal = "Science Advances",
    abstract = "The Siluro-Devonian adaptive radiation of jawed vertebrates, which underpins almost all living vertebrate biodiversity, is characterized by the evolutionary innovation of the lower jaw. Multiple lines of evidence have suggested that the jaw evolved from a rostral gill arch, but when the jaw took on a feeding function remains unclear. We quantified the variety of form in the earliest jaws in the fossil record from which we generated a theoretical morphospace that we then tested for functional optimality. By drawing comparisons with the real jaw data and reconstructed jaw morphologies from phylogenetically inferred ancestors, our results show that the earliest jaw shapes were optimized for fast closure and stress resistance, inferring a predatory feeding function. Jaw shapes became less optimal for these functions during the later radiation of jawed vertebrates. Thus, the evolution of jaw morphology has continually explored previously unoccupied morphospace and accumulated disparity through time, laying the foundation for diverse feeding strategies and the success of jawed vertebrates.",
    url = "https://doi.org/10.1126/sciadv.abl3644",
    doi = "10.1126/sciadv.abl3644",
    openalex = "W4221093256",
    references = "doi101016jpalaeo201612051, doi1010800272463420161111225, doi101093icb12177, doi101111j109636421996tb01658x, doi101111j146364091980tb00660x, doi101111pala12125, doi1016660022336020000740301etjftl20co2"
}

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

@article{doi101039d2cs00513a,
    author = "Yu, Han‐Ping and Zhu, Ying‐Jie",
    title = "Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong",
    year = "2024",
    journal = "Chemical Society Reviews",
    abstract = "Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.",
    url = "https://doi.org/10.1039/d2cs00513a",
    doi = "10.1039/d2cs00513a",
    openalex = "W4392950258",
    references = "doi101016jactbio202002019, doi101038s41467019121857"
}