Trilobites

@misc{walcott1918appendages5,
    author = "Walcott, C. D",
    title = "Appendages of trilobites. Cambrian Geology and Paleontology, IV",
    year = "1918",
    howpublished = "Smithsonian Miscellaneous Collections, v. 67, p. 115-216",
    note = "talkorigins\_source = {true}; raw\_reference = {Walcott, C. D., 1918, Appendages of trilobites. Cambrian Geology and Paleontology, IV: Smithsonian Miscellaneous Collections, v. 67, p. 115-216.}"
}

@misc{kauffman1933variationsstatistische2,
    author = "Kauffman, R",
    title = {Variations-statistische Untersuchungen ber die "Artabwandlung" und "Artumbildung" an der oberkambrischen Trilobitengattung Olenus Dalm},
    year = "1933",
    howpublished = "Geol. Pal. Inst. Univ. Griefswald, Abh., v. 10, p. 1-54",
    note = {talkorigins\_source = {true}; raw\_reference = {Kauffman, R., 1933, Variations-statistische Untersuchungen ber die "Artabwandlung" und "Artumbildung" an der oberkambrischen Trilobitengattung Olenus Dalm: Geol. Pal. Inst. Univ. Griefswald, Abh., v. 10, p. 1-54.}}
}

@misc{kauffman1935exaktstatistische3,
    author = "Kauffman, R",
    title = "Exakt-statistische Biostratigraphie der Olenus - Arten von Sudland",
    year = "1935",
    howpublished = "Geol. Foren. Stockholm Frhandl., v. 1935, p. 19-28",
    note = "talkorigins\_source = {true}; raw\_reference = {Kauffman, R., 1935, Exakt-statistische Biostratigraphie der Olenus - Arten von Sudland: Geol. Foren. Stockholm Frhandl., v. 1935, p. 19-28.}"
}

@misc{whittington1953silicified8,
    author = "Whittington, H. B. and Evitt, W. R. I. I",
    title = "Silicified Middle Ordovician trilobites",
    year = "1953",
    howpublished = "Geological Society of America Memoir 59",
    note = "talkorigins\_source = {true}; raw\_reference = {Whittington, H. B., and Evitt, W. R. I. I., 1953, Silicified Middle Ordovician trilobites. Geological Society of America Memoir 59.}"
}

@misc{strmer1959trilobitoidea4,
    author = "Strmer, L",
    title = "Trilobitoidea, in Moore, R. C., ed., Treatise on Invertebrate Paleontology, Part O, Arthropoda I",
    year = "1959",
    howpublished = "p. 23-37",
    note = "talkorigins\_source = {true}; raw\_reference = {Strmer, L., 1959, Trilobitoidea, in Moore, R. C., ed., Treatise on Invertebrate Paleontology, Part O, Arthropoda I: p. 23-37.}"
}

@article{grant1962trilobite1,
    author = "Grant, R. E",
    title = "Trilobite distribution, upper Franconia Formation (Upper Cambrian), southeastern Minnesota",
    year = "1962",
    journal = "Journal of Paleontology, v. 36, p. 965- 998",
    note = "talkorigins\_source = {true}; raw\_reference = {Grant, R. E., 1962, Trilobite distribution, upper Franconia Formation (Upper Cambrian), southeastern Minnesota: Journal of Paleontology, v. 36, p. 965- 998.}"
}

@misc{fritz1968middle,
    author = "Fritz, W H",
    title = "Middle Cambrian Trilobite Studies near Field, British Columbia",
    year = "1968",
    url = "https://doi.org/10.4095/106307",
    doi = "10.4095/106307"
}

@incollection{whittington1975trilobites,
    author = "Whittington, Harry B.",
    title = "Trilobites with appendages from the Middle Cambrian, Burgess Shale, British Columbia",
    year = "1975",
    booktitle = "Fossils and Strata",
    url = "https://doi.org/10.18261/8200049639-1975-06",
    doi = "10.18261/8200049639-1975-06",
    pages = "97-136"
}

@misc{whittington1975trilobites6,
    author = "Whittington, H. B",
    title = "Trilobites with appendages from the Middle Cambrian, Burgess Shale, British Columbia",
    year = "1975",
    howpublished = "Fossils and Strata (Oslo), v. 4, p. 97- 136",
    note = "talkorigins\_source = {true}; raw\_reference = {Whittington, H. B., 1975, Trilobites with appendages from the Middle Cambrian, Burgess Shale, British Columbia: Fossils and Strata (Oslo), v. 4, p. 97- 136.}"
}

A study of new specimens of the bivalved arthropod Protocaris preriosa Resser, 1929 from the Burgess Shale has added much information to the original description, and the species is removed to a new genus Bra11c/1iocaris. Prorocaris marshi Walcott, 1884 and Dioxycaris arge11ra (Walcott, 1886) are also redescribed to facilitate comparison. The cephalic region of Bra11chiocaris preriosa bore a paired antenna anterior to a pair of stout appendages which may have been chelate. Suboval valves, the dorsal margin terminating anteriorly and posteriorly in a small pointed process, covered the anterior of the body. The trunk included about 46 divisions followed by a telson bearing a pair of short pointed processes. The lamellate trunk appendages may have been biramous, with a short, segmented proximal element. The animal probably swam near the seabed by metachronal movements of the lamellate appendages, which may also have functioned in respiration. B. pretiosa shows closest affinities to the branchiopod Crustacea among extant arthropods but is considered unlikely to represent a direct evolutionary predecessor of this group. The trunk of Protocaris marshi included about 65 divisions; the tel son processes were elongate and curved. The appendages are unknown. The carapace of Dioxycaris arge11ta is similar in outline and size to that of Branchiocaris preliosa but the only known specimen is poorly preserved and lacks evidence of the soft-part morphology.

@misc{briggs1976the,
    author = "Briggs, D E G",
    title = "The Arthropod Branchiocaris N. Gen., Middle Cambrian, Burgess Shale, British Columbia",
    year = "1976",
    abstract = "A study of new specimens of the bivalved arthropod Protocaris preriosa Resser, 1929 from the Burgess Shale has added much information to the original description, and the species is removed to a new genus Bra11c/1iocaris. Prorocaris marshi Walcott, 1884 and Dioxycaris arge11ra (Walcott, 1886) are also redescribed to facilitate comparison. The cephalic region of Bra11chiocaris preriosa bore a paired antenna anterior to a pair of stout appendages which may have been chelate. Suboval valves, the dorsal margin terminating anteriorly and posteriorly in a small pointed process, covered the anterior of the body. The trunk included about 46 divisions followed by a telson bearing a pair of short pointed processes. The lamellate trunk appendages may have been biramous, with a short, segmented proximal element. The animal probably swam near the seabed by metachronal movements of the lamellate appendages, which may also have functioned in respiration. B. pretiosa shows closest affinities to the branchiopod Crustacea among extant arthropods but is considered unlikely to represent a direct evolutionary predecessor of this group. The trunk of Protocaris marshi included about 65 divisions; the tel son processes were elongate and curved. The appendages are unknown. The carapace of Dioxycaris arge11ta is similar in outline and size to that of Branchiocaris preliosa but the only known specimen is poorly preserved and lacks evidence of the soft-part morphology.",
    url = "https://doi.org/10.4095/103962",
    doi = "10.4095/103962"
}

The type species of the genus, N.compacta, is described from new preparations and measurements of over 100 specimens from C. D. Walcott’s original collection, and 5 from the recent re-investigation. Photographs and explanatory drawings provide the basis for considerations of mode of preservation, and lead to a new reconstruction. The dorsal exoskeleton was divided by a single articulation into two shields, each moderately convex with a raised axial region, the subcircular anterior shield overlapping for a short distance the longer posterior shield; narrow reflexed doublure on both shields. Dorsal surfaces of shields smooth, without transverse furrows, eyes absent. Axial region of anterior shield widest posteriorly, extending forward to threequarters length of shield, labrum may have been present under anterior portion. Axial region of posterior shield tapered back, reaching close to posterior margin of shield. Alimentary canal may be preserved filled with sediment, and was probably U-shaped anteriorly, broadest beneath anterior portion of axial region, tapering back to tip of posterior shield. Two types of alimentary diverticula preserved as reflective bands on anterior shield; single trunk of lateral diverticula ran transversely at mid-length and ramified beneath lateral region of shield; three pairs of axial diverticula, one per segment, originated behind main trunk of lateral diverticula and ramified in posterior part of axial region. Axial diverticula, one per segment and not ramifying, appear to have been present beneath the axial region of the posterior shield. Paired areas of muscle attachment, preserved as reflective or pyritous areas, are segmentally arranged along the axial region, one pair close together at the anterior extremity. One pair of long, uniramous, multi-jointed antennae was attached beside anterior extremity of axial region, followed by a maximum of 19 pairs of similar biramous appendages, three pairs on the posterior part of the anterior shield, remainder beneath posterior shield. Large triangular coxa strongly spinose on adaxial margin; inner, leg branch of five podomeres and terminal, thorn-like spine; large, spinose endite on proximal podomere. Outer branch arose from abaxial, dorsal margin of coxa, and consisted of slim, tapering shaft with terminal lobe, dorsal margin of shaft bore many long, thin, upward and backwardly directed lamellae. Specimens range in length from 9 to 40 mm, some 40 % of the sample being cast dorsal exoskeletons, the remainder whole animals. About one-fifth of the sample bore a posterolateral spine on the anterior shield, rather than having a rounded angle. This difference was recently used to erect two new species, Naraoia halia and N. pammon; here it is taken as the sole evidence of dimorphism in the single species N. compacta. A second species, N. spinfer, is recognized from two poorly-preserved specimens, characterized by seven pairs of lateral spines and a median posterior spine on the margins of the posterior shield; the axial region is poorly defined and appendages virtually unknown. N. compacta is considered to have been a benthonic predator and scavenger, walking, digging and raking in search of food much as did the trilobite Olenoides serratus, and to have had poor swimming powers. The lamellate outer branch of the appendage is regarded as a gill branch, aerated by currents produced when walking and swimming or drifting. There is no evidence of an abdomen or telson, so that N. compacta is a trilobite-like animal lacking the articulated thorax; it is regarded as representing a separate order of class Trilobita.

@article{whittington1977the,
    author = "Whittington, Harry Blackmore",
    title = "The Middle Cambrian trilobite Naraoia, Burgess Shale, British Columbia",
    year = "1977",
    journal = "Philosophical Transactions of the Royal Society of London. B, Biological Sciences",
    abstract = "The type species of the genus, N.compacta, is described from new preparations and measurements of over 100 specimens from C. D. Walcott’s original collection, and 5 from the recent re-investigation. Photographs and explanatory drawings provide the basis for considerations of mode of preservation, and lead to a new reconstruction. The dorsal exoskeleton was divided by a single articulation into two shields, each moderately convex with a raised axial region, the subcircular anterior shield overlapping for a short distance the longer posterior shield; narrow reflexed doublure on both shields. Dorsal surfaces of shields smooth, without transverse furrows, eyes absent. Axial region of anterior shield widest posteriorly, extending forward to threequarters length of shield, labrum may have been present under anterior portion. Axial region of posterior shield tapered back, reaching close to posterior margin of shield. Alimentary canal may be preserved filled with sediment, and was probably U-shaped anteriorly, broadest beneath anterior portion of axial region, tapering back to tip of posterior shield. Two types of alimentary diverticula preserved as reflective bands on anterior shield; single trunk of lateral diverticula ran transversely at mid-length and ramified beneath lateral region of shield; three pairs of axial diverticula, one per segment, originated behind main trunk of lateral diverticula and ramified in posterior part of axial region. Axial diverticula, one per segment and not ramifying, appear to have been present beneath the axial region of the posterior shield. Paired areas of muscle attachment, preserved as reflective or pyritous areas, are segmentally arranged along the axial region, one pair close together at the anterior extremity. One pair of long, uniramous, multi-jointed antennae was attached beside anterior extremity of axial region, followed by a maximum of 19 pairs of similar biramous appendages, three pairs on the posterior part of the anterior shield, remainder beneath posterior shield. Large triangular coxa strongly spinose on adaxial margin; inner, leg branch of five podomeres and terminal, thorn-like spine; large, spinose endite on proximal podomere. Outer branch arose from abaxial, dorsal margin of coxa, and consisted of slim, tapering shaft with terminal lobe, dorsal margin of shaft bore many long, thin, upward and backwardly directed lamellae. Specimens range in length from 9 to 40 mm, some 40 \% of the sample being cast dorsal exoskeletons, the remainder whole animals. About one-fifth of the sample bore a posterolateral spine on the anterior shield, rather than having a rounded angle. This difference was recently used to erect two new species, Naraoia halia and N. pammon; here it is taken as the sole evidence of dimorphism in the single species N. compacta. A second species, N. spinfer, is recognized from two poorly-preserved specimens, characterized by seven pairs of lateral spines and a median posterior spine on the margins of the posterior shield; the axial region is poorly defined and appendages virtually unknown. N. compacta is considered to have been a benthonic predator and scavenger, walking, digging and raking in search of food much as did the trilobite Olenoides serratus, and to have had poor swimming powers. The lamellate outer branch of the appendage is regarded as a gill branch, aerated by currents produced when walking and swimming or drifting. There is no evidence of an abdomen or telson, so that N. compacta is a trilobite-like animal lacking the articulated thorax; it is regarded as representing a separate order of class Trilobita.",
    url = "https://doi.org/10.1098/rstb.1977.0117",
    doi = "10.1098/rstb.1977.0117",
    number = "974",
    pages = "409-443",
    volume = "280"
}

The Burgess Shale (Middle Cambrian) polychaetes Canadia spinosa Walcott, Burgessochaeta setigera (Walcott) gen. nov. and Peronochaeta dubia (Walcott) gen. nov. are redescribed on the basis of Walcott’s type specimens and on much additional material. Two new polychaetes Insolicorypha psygma gen. et sp. nov. and Stephenoscolex argutus gen. et sp. nov. are described. A poorly preserved specimen of unknown generic affinity is described as type A. The polychaetes are preserved as thin films that adhere to both sides of the split in the rock so that part and counterpart may be available. In C. spinosa, B. setigera and I. psygma, parts of the bodies such as the fascicles of setae are separated by thin layers of sediment that apparently seeped in during turbulent transport in turbidites or mudflows. The bodies therefore lie on two or more planes of microbedding and the factors that control exposure across a specimen are discussed. Aspects of the palaeoecology of the Burgess Shale are reviewed, including the distance the biota was transported prior to burial, the reasons for the exquisite preservation, and the effects of sedimentary compaction. C. spinosa was characterized by broad notosetae that extended across the dorsum, and large fascicles of neurosetae. Lobate branchiae were situated in the inter-ramal spaces. The prostomium bore a pair of elongate tentacles and the straight gut had an eversible unarmed proboscis. Several lines of evidence suggest that C. spinosa was an active benthonic swimmer. B. setigera was peculiar in possessing identical notosetae and neurosetae along the entire body. Long anterior tentacles, possibly of peristomial origin, may have been used in feeding. Indirect evidence indicates that B. setigera inhabited a burrow which it might have excavated with its proboscis. P. dubia may also have burrowed but it had uniramous parapodia bearing simple and acicular setae. The prostomium bore a pair of short appendages. I. psygma had extended neuropodia bearing cirri and elongate setae. The notopodia were reduced and cirri appear to have been wanting. The peculiar prostomium carried a pair of appendages. I. psygma is regarded as a pelagic polychaete. S. argutus possessed uniramous parapodia with simple stout setae. The bilobed prostomium bore at least one pair, and perhaps three pairs, of short appendages. Type A was the largest of the Burgess Shale polychaetes and had prominent setae on at least the anterior section of the body. Type A was a sediment eater but the feeding habits of the other polychaetes are uncertain. Particular attention is given to the influence of decay on the Burgess Shale polychaetes. To place the Burgess Shale polychaetes in some geological perspective other Cambrian worms, including a polychaete from the Spence Shale of Utah, are briefly redescribed and the late Precambrian (Ediacarian) worms Dickinsonia, Spriggina and Marywadea are assessed. Contrary to the findings of other workers, no convincing evidence for placing these latter worms in the polychaetes is forthcoming.

@article{conwaymorris1979middle,
    author = "Conway Morris, Simon",
    title = "Middle Cambrian polychaetes from the Burgess Shale of British Columbia",
    year = "1979",
    journal = "Philosophical Transactions of the Royal Society of London. B, Biological Sciences",
    abstract = "The Burgess Shale (Middle Cambrian) polychaetes Canadia spinosa Walcott, Burgessochaeta setigera (Walcott) gen. nov. and Peronochaeta dubia (Walcott) gen. nov. are redescribed on the basis of Walcott’s type specimens and on much additional material. Two new polychaetes Insolicorypha psygma gen. et sp. nov. and Stephenoscolex argutus gen. et sp. nov. are described. A poorly preserved specimen of unknown generic affinity is described as type A. The polychaetes are preserved as thin films that adhere to both sides of the split in the rock so that part and counterpart may be available. In C. spinosa, B. setigera and I. psygma, parts of the bodies such as the fascicles of setae are separated by thin layers of sediment that apparently seeped in during turbulent transport in turbidites or mudflows. The bodies therefore lie on two or more planes of microbedding and the factors that control exposure across a specimen are discussed. Aspects of the palaeoecology of the Burgess Shale are reviewed, including the distance the biota was transported prior to burial, the reasons for the exquisite preservation, and the effects of sedimentary compaction. C. spinosa was characterized by broad notosetae that extended across the dorsum, and large fascicles of neurosetae. Lobate branchiae were situated in the inter-ramal spaces. The prostomium bore a pair of elongate tentacles and the straight gut had an eversible unarmed proboscis. Several lines of evidence suggest that C. spinosa was an active benthonic swimmer. B. setigera was peculiar in possessing identical notosetae and neurosetae along the entire body. Long anterior tentacles, possibly of peristomial origin, may have been used in feeding. Indirect evidence indicates that B. setigera inhabited a burrow which it might have excavated with its proboscis. P. dubia may also have burrowed but it had uniramous parapodia bearing simple and acicular setae. The prostomium bore a pair of short appendages. I. psygma had extended neuropodia bearing cirri and elongate setae. The notopodia were reduced and cirri appear to have been wanting. The peculiar prostomium carried a pair of appendages. I. psygma is regarded as a pelagic polychaete. S. argutus possessed uniramous parapodia with simple stout setae. The bilobed prostomium bore at least one pair, and perhaps three pairs, of short appendages. Type A was the largest of the Burgess Shale polychaetes and had prominent setae on at least the anterior section of the body. Type A was a sediment eater but the feeding habits of the other polychaetes are uncertain. Particular attention is given to the influence of decay on the Burgess Shale polychaetes. To place the Burgess Shale polychaetes in some geological perspective other Cambrian worms, including a polychaete from the Spence Shale of Utah, are briefly redescribed and the late Precambrian (Ediacarian) worms Dickinsonia, Spriggina and Marywadea are assessed. Contrary to the findings of other workers, no convincing evidence for placing these latter worms in the polychaetes is forthcoming.",
    url = "https://doi.org/10.1098/rstb.1979.0006",
    doi = "10.1098/rstb.1979.0006",
    number = "1007",
    pages = "227-274",
    volume = "285"
}

Six species of arthropods from the Walcott Collection, U.S. National Museum, are described. Molaria spinifera Walcott is known from over 100 specimens, a sample that reveals the morphology fairly fully. Between one and 12 specimens of the other species are known, and yield limited information. M. spinifera had a smooth, convex exoskeleton, not trilobed, the cephalic shield being a quarter-sphere in shape, eight trunk tergites diminishing in size posteriorly and the cylindrical telson having a short ventral spine and a long, jointed posterior spine. The cephalon bore a pair of short, slim antennae and three pairs of biramous appendages. There were eight pairs of similar biramous appendages on the trunk. The biramous appendage had a large basal podomere, a segmented inner walking branch, and a lobate outer branch arising from the basal podomere and bearing marginal lamellae. The sagittal length of cephalon, trunk and telson ranged from 8 to 26 mm, the posterior spine slightly exceeding this length; the smallest specimens are similar to the largest. The animal lacked eyes, and was probably benthic and may have been a scavenger and deposit feeder. Habelia optata Walcott was superficially similar to M. spinfera, the trunk being of 12 tergites; there was no cylindrical telson, but a ridged and barbed spine inserted into the 12th tergite, the spine having a joint at about two-thirds its length. The external surface of the exoskeleton was tuberculate; the pleurae of the tergites curved back increasingly strongly posteriorly, the tips being spinose. The cephalon appears to have borne a slim, short pair of antennae and two pairs of biramous appendages; the proximal portions of the jointed inner branches may have been adapted for grinding food. The first six trunk somites bore biramous limbs, the inner branch being a relatively long walking leg, the outer a lobe having marginal lamellae; on the posterior trunk somites there is no trace of the inner branch, but the outer was present. H. optata lacked eyes and was probably a benthic animal. Only the smooth exoskeleton of a possible second species, H? brevicauda Simonetta, is known, of which the posterior spine is short and bluntly rounded. The new genus and species Sarotrocercus oblita is erected for a few specimens, in which the body is about 1 cm in length, and behind which is a slim spine having a group of spines at the tip. From beneath the anterolateral margin of the cephalic shield a large eye projected, and the cephalon bore also one pair of large, jointed appendages. Behind these were pairs of lobed appendages bearing marginal lamellae, one on the cephalon and one on each of the nine trunk somites. This small species may have drifted and swum in the higher water layers, the occasional carcass lying on the sea bottom having been preserved. The single specimen of Actaeus armatus Simonetta is over 6 cm in length. The exoskeleton of this specimen is divided into cephalic shield with marginal eye lobe, 11 trunk tergites and a triangular terminal plate. The anterior cephalic appendage was Leanchoil-like, the stout proximal portion being curved and ending in a group of claws, the next two podomeres bearing long, slim extensions. The head shield also bore three pairs of biramous appendages, consisting of a small jointed inner branch and a large lobed outer branch with marginal lamellae; appendages like these outer branches are preserved beneath the trunk tergites. Only two specimens are identified as Alalcomenaeus cambricus Simonetta (length 3-4 cm). The exoskeleton is divisible into cephalic shield, trunk of probably 12 tergites, and an ovate terminal plate which has lateral bands. The cephalon has a marginal eye lobe and an anterior appendage which is broad proximally, the long distal portion being slim. The holotype shows a series of lobed appendages, the first three cephalic. Between them project the curved, pointed terminations of inner branches. The second specimen suggests that these lobed appendages bore marginal filaments, and reveals the inner branches as blade-shaped, and spinose on the inward-facing margin. These biramous appendages were present on all the trunk somites, being largest anteriorly. These remarkable appendages suggest a benthic scavenger, able to hold on to, and tear up, a carcass. ‘ Leanchoilia protogonia ’ Simonetta is most probably a composite, a poorly preserved Leanchoilia superlata lying on an unidentified, branching organism. The five species showing appendages extend greatly the known range of variation in morphology of the Burgess Shale arthropods. Affinities are discussed, but familial and higher classification is postponed, pending completion of work on all the arthropods from the shale.

@article{whittington1981rare,
    author = "Whittington, Harry Blackmore",
    title = "Rare arthropods from the Burgess Shale, Middle Cambrian, British Columbia",
    year = "1981",
    journal = "Philosophical Transactions of the Royal Society of London. B, Biological Sciences",
    abstract = "Six species of arthropods from the Walcott Collection, U.S. National Museum, are described. Molaria spinifera Walcott is known from over 100 specimens, a sample that reveals the morphology fairly fully. Between one and 12 specimens of the other species are known, and yield limited information. M. spinifera had a smooth, convex exoskeleton, not trilobed, the cephalic shield being a quarter-sphere in shape, eight trunk tergites diminishing in size posteriorly and the cylindrical telson having a short ventral spine and a long, jointed posterior spine. The cephalon bore a pair of short, slim antennae and three pairs of biramous appendages. There were eight pairs of similar biramous appendages on the trunk. The biramous appendage had a large basal podomere, a segmented inner walking branch, and a lobate outer branch arising from the basal podomere and bearing marginal lamellae. The sagittal length of cephalon, trunk and telson ranged from 8 to 26 mm, the posterior spine slightly exceeding this length; the smallest specimens are similar to the largest. The animal lacked eyes, and was probably benthic and may have been a scavenger and deposit feeder. Habelia optata Walcott was superficially similar to M. spinfera, the trunk being of 12 tergites; there was no cylindrical telson, but a ridged and barbed spine inserted into the 12th tergite, the spine having a joint at about two-thirds its length. The external surface of the exoskeleton was tuberculate; the pleurae of the tergites curved back increasingly strongly posteriorly, the tips being spinose. The cephalon appears to have borne a slim, short pair of antennae and two pairs of biramous appendages; the proximal portions of the jointed inner branches may have been adapted for grinding food. The first six trunk somites bore biramous limbs, the inner branch being a relatively long walking leg, the outer a lobe having marginal lamellae; on the posterior trunk somites there is no trace of the inner branch, but the outer was present. H. optata lacked eyes and was probably a benthic animal. Only the smooth exoskeleton of a possible second species, H? brevicauda Simonetta, is known, of which the posterior spine is short and bluntly rounded. The new genus and species Sarotrocercus oblita is erected for a few specimens, in which the body is about 1 cm in length, and behind which is a slim spine having a group of spines at the tip. From beneath the anterolateral margin of the cephalic shield a large eye projected, and the cephalon bore also one pair of large, jointed appendages. Behind these were pairs of lobed appendages bearing marginal lamellae, one on the cephalon and one on each of the nine trunk somites. This small species may have drifted and swum in the higher water layers, the occasional carcass lying on the sea bottom having been preserved. The single specimen of Actaeus armatus Simonetta is over 6 cm in length. The exoskeleton of this specimen is divided into cephalic shield with marginal eye lobe, 11 trunk tergites and a triangular terminal plate. The anterior cephalic appendage was Leanchoil-like, the stout proximal portion being curved and ending in a group of claws, the next two podomeres bearing long, slim extensions. The head shield also bore three pairs of biramous appendages, consisting of a small jointed inner branch and a large lobed outer branch with marginal lamellae; appendages like these outer branches are preserved beneath the trunk tergites. Only two specimens are identified as Alalcomenaeus cambricus Simonetta (length 3-4 cm). The exoskeleton is divisible into cephalic shield, trunk of probably 12 tergites, and an ovate terminal plate which has lateral bands. The cephalon has a marginal eye lobe and an anterior appendage which is broad proximally, the long distal portion being slim. The holotype shows a series of lobed appendages, the first three cephalic. Between them project the curved, pointed terminations of inner branches. The second specimen suggests that these lobed appendages bore marginal filaments, and reveals the inner branches as blade-shaped, and spinose on the inward-facing margin. These biramous appendages were present on all the trunk somites, being largest anteriorly. These remarkable appendages suggest a benthic scavenger, able to hold on to, and tear up, a carcass. ‘ Leanchoilia protogonia ’ Simonetta is most probably a composite, a poorly preserved Leanchoilia superlata lying on an unidentified, branching organism. The five species showing appendages extend greatly the known range of variation in morphology of the Burgess Shale arthropods. Affinities are discussed, but familial and higher classification is postponed, pending completion of work on all the arthropods from the shale.",
    url = "https://doi.org/10.1098/rstb.1981.0033",
    doi = "10.1098/rstb.1981.0033",
    number = "1060",
    pages = "329-357",
    volume = "292"
}

@article{whittington1985tegopelte7,
    author = "Whittington, H. B",
    title = "Tegopelte gigas, a second soft-bodied trilobite from the Burgess Shale, Middle Cambrian, British Columbia",
    year = "1985",
    journal = "Journal of Paleontology, v. 59, p. 1251-1274",
    note = "talkorigins\_source = {true}; raw\_reference = {Whittington, H. B., 1985, Tegopelte gigas, a second soft-bodied trilobite from the Burgess Shale, Middle Cambrian, British Columbia: Journal of Paleontology, v. 59, p. 1251-1274.}"
}

@misc{zhangwentang1985preliminary9,
    author = "Zhang Wen-tang, Hou Xian-guang",
    title = "Preliminary notes on the occurance of the unusual trilobite Naraoia in Asia [in Chinese]",
    year = "1985",
    howpublished = "Acta Palaeontologica Sinica, v. 24, p. 591-595",
    note = "talkorigins\_source = {true}; raw\_reference = {Zhang Wen-tang, and Hou Xian-guang, 1985, Preliminary notes on the occurance of the unusual trilobite Naraoia in Asia [in Chinese]: Acta Palaeontologica Sinica, v. 24, p. 591-595.}"
}

@article{esteve2012intraspecific,
    author = "Esteve, Jorge",
    title = "Intraspecific variability in paradoxidid trilobites from the Purujosa trilobite assemblage (middle Cambrian, northeast Spain)",
    year = "2012",
    journal = "Acta Palaeontologica Polonica",
    url = "https://doi.org/10.4202/app.2012.0006",
    doi = "10.4202/app.2012.0006"
}

The feeding ecology of the 505-million-year-old arthropod Sidneyia inexpectans from the middle Cambrian (Series 3, Stage 5) Burgess Shale fauna (British Columbia, Canada) is revealed by three lines of evidence: the structure of its digestive system, the fossilized contents of its gut and the functional anatomy of its appendages. The digestive tract of Sidneyia is straight, tubular and relatively narrow in the trunk region. It is enlarged into a pear-shaped area in the cephalic region and stretches notably to form a large pocket in the abdomen. The mouth is ventral, posteriorly directed and leads to the midgut via a short tubular structure interpreted as the oesophagus. Anteriorly, three pairs of glands with internal, branching tubular structures open into the digestive tract. These glands have equivalents in various Cambrian arthropod taxa (e.g. naraoiids) and modern arthropods. Their primary function was most likely to digest and assimilate food. The abdominal pocket of Sidneyia concentrates undigested skeletal elements and various residues. It is interpreted here as the functional analogue of the stercoral pocket of some extant terrestrial arachnids (e.g. Araneae, Solifugae), whose primary function is to store food residuals and excretory material until defecation. Analysis of the gut contents indicates that Sidneyia fed largely on small ptychopariid trilobites, brachiopods, possibly agnostids, worms and other undetermined animals. Sidneyia was primarily a durophagous carnivore with predatory and/or scavenging habits, feeding on small invertebrates that lived at the water-sediment interface. There is no evidence for selective feeding. Its food items (e.g. living prey or dead material) were grasped and manipulated ventrally by its anterior appendages, then macerated into ingestible fragments and conveyed to the mouth via the converging action of strong molar-like gnathobases. Digestion probably took place within the anterior midgut via enzymes secreted in the glands. Residues were transported through the digestive tract into the abdominal pocket. The storage of faeces suggests infrequent feeding. The early diagenetic three-dimensional preservation of the digestive glands and abdominal pocket may be due to the capacity of Sidneyia to store Phosphorus and Calcium (e.g. spherites) in its digestive tissues during life as do, for example, modern horseshoe crabs.

@article{doi101016jasd201509003,
    author = "Zacaï, Axelle and Vannier, Jean and Lerosey-Aubril, Rudy",
    title = "Reconstructing the diet of a 505-million-year-old arthropod: Sidneyia inexpectans from the Burgess Shale fauna.",
    year = "2016",
    journal = "Arthropod structure \& development",
    abstract = "The feeding ecology of the 505-million-year-old arthropod Sidneyia inexpectans from the middle Cambrian (Series 3, Stage 5) Burgess Shale fauna (British Columbia, Canada) is revealed by three lines of evidence: the structure of its digestive system, the fossilized contents of its gut and the functional anatomy of its appendages. The digestive tract of Sidneyia is straight, tubular and relatively narrow in the trunk region. It is enlarged into a pear-shaped area in the cephalic region and stretches notably to form a large pocket in the abdomen. The mouth is ventral, posteriorly directed and leads to the midgut via a short tubular structure interpreted as the oesophagus. Anteriorly, three pairs of glands with internal, branching tubular structures open into the digestive tract. These glands have equivalents in various Cambrian arthropod taxa (e.g. naraoiids) and modern arthropods. Their primary function was most likely to digest and assimilate food. The abdominal pocket of Sidneyia concentrates undigested skeletal elements and various residues. It is interpreted here as the functional analogue of the stercoral pocket of some extant terrestrial arachnids (e.g. Araneae, Solifugae), whose primary function is to store food residuals and excretory material until defecation. Analysis of the gut contents indicates that Sidneyia fed largely on small ptychopariid trilobites, brachiopods, possibly agnostids, worms and other undetermined animals. Sidneyia was primarily a durophagous carnivore with predatory and/or scavenging habits, feeding on small invertebrates that lived at the water-sediment interface. There is no evidence for selective feeding. Its food items (e.g. living prey or dead material) were grasped and manipulated ventrally by its anterior appendages, then macerated into ingestible fragments and conveyed to the mouth via the converging action of strong molar-like gnathobases. Digestion probably took place within the anterior midgut via enzymes secreted in the glands. Residues were transported through the digestive tract into the abdominal pocket. The storage of faeces suggests infrequent feeding. The early diagenetic three-dimensional preservation of the digestive glands and abdominal pocket may be due to the capacity of Sidneyia to store Phosphorus and Calcium (e.g. spherites) in its digestive tissues during life as do, for example, modern horseshoe crabs.",
    url = "https://pubmed.ncbi.nlm.nih.gov/26410799/",
    doi = "10.1016/j.asd.2015.09.003",
    pmid = "26410799"
}

Agnostids (agnostinids and eodiscinids) are a widespread and biostratigraphically important group of Cambro-Ordovician euarthropods whose evolutionary affinities have been highly controversial. Their dumbbell-shaped calcified tergum was traditionally suggested to unite them with trilobites, but agnostinids have alternatively been interpreted as stem-crustaceans, based on Orsten larval material from the Cambrian of Sweden. We describe exceptionally preserved soft tissues from mature individuals of the agnostinids Peronopsis and Ptychagnostus from the middle Cambrian (Wuliuan Stage) Burgess Shale (Walcott Quarry and Marble Canyon, British Columbia, Canada), facilitating the testing of alternative hypotheses. The digestive tract includes conspicuous ramifying cephalic diverticulae. The cephalon carries one pair of elongate spinous antennules projecting to the front, two pairs of appendages with distally setose, oar-like exopods, and three pairs of presumably biramous appendages with endopods sporting club-shaped exites. The trunk bears five appendage pairs, at least the first two of which are similar to the posteriormost cephalic pairs. The combined evidence supports a nektobenthic and detritivorous lifestyle for agnostinids. A head with six appendiferous segments contrasts strikingly with the four known in trilobites and five typical of mandibulates. Agnostinids are retrieved as the sister group to polymeroid trilobites in our phylogeny, implying that crustacean-like morphologies evolved homoplastically. This result highlights the variability in segmental composition of the artiopodan head. Finally, our study emphasizes the continued role of Burgess Shale-type fossils in resolving the affinities of problematic biomineralizing taxa.

@article{doi101098rspb20182314,
    author = "Moysiuk, J and Caron, J-B",
    title = "Burgess Shale fossils shed light on the agnostid problem.",
    year = "2019",
    journal = "Proceedings. Biological sciences",
    abstract = "Agnostids (agnostinids and eodiscinids) are a widespread and biostratigraphically important group of Cambro-Ordovician euarthropods whose evolutionary affinities have been highly controversial. Their dumbbell-shaped calcified tergum was traditionally suggested to unite them with trilobites, but agnostinids have alternatively been interpreted as stem-crustaceans, based on Orsten larval material from the Cambrian of Sweden. We describe exceptionally preserved soft tissues from mature individuals of the agnostinids Peronopsis and Ptychagnostus from the middle Cambrian (Wuliuan Stage) Burgess Shale (Walcott Quarry and Marble Canyon, British Columbia, Canada), facilitating the testing of alternative hypotheses. The digestive tract includes conspicuous ramifying cephalic diverticulae. The cephalon carries one pair of elongate spinous antennules projecting to the front, two pairs of appendages with distally setose, oar-like exopods, and three pairs of presumably biramous appendages with endopods sporting club-shaped exites. The trunk bears five appendage pairs, at least the first two of which are similar to the posteriormost cephalic pairs. The combined evidence supports a nektobenthic and detritivorous lifestyle for agnostinids. A head with six appendiferous segments contrasts strikingly with the four known in trilobites and five typical of mandibulates. Agnostinids are retrieved as the sister group to polymeroid trilobites in our phylogeny, implying that crustacean-like morphologies evolved homoplastically. This result highlights the variability in segmental composition of the artiopodan head. Finally, our study emphasizes the continued role of Burgess Shale-type fossils in resolving the affinities of problematic biomineralizing taxa.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC6367181/",
    doi = "10.1098/rspb.2018.2314",
    pmcid = "PMC6367181",
    pmid = "30963877"
}

@inproceedings{andlosso2021clasperlike,
    author = "Losso, Sarah and Ortega-Hernandez, Javier",
    title = "CLASPER-LIKE APPENDAGES IN THE MID-CAMBRIAN TRILOBITE OLENOIDES SERRATUS FROM THE BURGESS SHALE",
    year = "2021",
    booktitle = "Geological Society of America Abstracts with Programs",
    url = "https://doi.org/10.1130/abs/2021am-365778",
    doi = "10.1130/abs/2021am-365778"
}