"The early evolution of the artiodactyls is fairly well documented by both the dentition and the skeletal material and provides the basis for fairly detailed analysis of evolutionary patterns....the origin of nearly all the recognized families can be traced to the late Middle Eocene or the Upper Eocene..." (Carroll, 1988)
GAP: No artiodactyl fossils known from the late Paleocene. Similar late Paleocene gaps in rodents, lagomorphs, and perissodactyls are currently being filled with newly discovered Asian fossils, so apparently much late Paleocene herbivore evolution occurred in central Asia. Perhaps the new Asian expeditions will find Paleocene artiodactyl fossils too. At any rate, somewhere between Chriacus & Diacodexis, the hind leg changed, particularly the ankle, to allow smooth running.
Hippos & pigs:
Ruminants: (see Scott & Janis, in Szalay et al., 1993, for details)
It's been very difficult to untangle the phylogeny of this fantastically huge, diverse, and successful group of herbivores. From the Eocene on, there are dozens of similar species, only some of them leading to modern lineages, with others in dozens of varied offshoot groups. Only recently have the main outlines become clear. The phylogeny listed below will probably change a bit as new information comes in.
Species-species transitions in artiodactyls:
This concludes our tour of the Cenozoic placental mammal record! However, please do not unfasten your seatbelts until the FAQ has come to a complete stop.
A quote from Gingerich (1985) about Eocene mammals also applies to the mammal record as a whole: "The fossil record of early Eocene mammals appears to be both gradual and punctuated. It is gradual in the sense that early and late representatives of all species, whether changing or not, are connected by intermediate forms. Some ancestor-descendant pairs of species are also connected by intermediates. The record is punctuated in the sense that new lineages appear abruptly at the Clarkforkian-Wasatchian boundary, and some possible ancestor-descendant pairs of species are not connected by intermediates."
In summary, as Carroll (1988) said, "There is considerable evidence from Tertiary mammals that significant change does occur during the duration of species, as they are typically recognized, and this change can account for the emergence of new species and genera."
I've tried to present a reasonably complete picture of the vertebrate record as it is now known. As extensive as it may seem, this is still just a crude summary, and I had to leave out some very large groups. For instance, notice that this list mostly includes transitional fossils that happened to lead to modern, familiar animals. This may unintentionally give the impression that fossil lineages proceed in a "straight line" from one fossil to the next. That's not so; generally at any one time there are a whole raft of successful species, only a few of which happened to leave modern descendents. The horse family is a good example; Merychippus gave rise to something like 19 new three- toed grazing horse species, which traveled all over the Old and New Worlds and were very successful at the time. Only one of these lines happened to lead to Equus, though, so that's the only line I described. As they say, "Evolution is not a ladder, it's a branching bush."
Since then, many more transitional fossils have been found, as sketched out in this FAQ. Typically, the only people who still demand to see transitional fossils are either unaware of the currently known fossil record (often due to the shoddy and very dated arguments presented in current creationist articles) or are unwilling to believe it for some reason.
I think the most noticeable aspects of the vertebrate fossil record, those which must be explained by any good model of the development of life on earth, are:
And now we come to the main question. Which of the many theories of the origins of life on earth are consistent with the known vertebrate fossil record, and explain its major features? I'll go back to the two main models I outlined at the beginning, creationism and evolution, and break them down further into several different possibilities. I'll try to summarize what they say, and whether or not they are consistent with the major features of the fossil record.
Evolution of all vertebrates by descent from a common ancestor, with change occurring both through punctuated equilibrium and gradual evolution, and with both modes of species formation (anagenesis and cladogenesis). These mechanisms and modes are consistent with (and in fact are predicted by) what is presently known about mutation, developmental biology, and population genetics According to this model, the remaining gaps in the fossil record are primarily due to the chance events of fossilization (particularly significant if evolution occurs locally or rapidly), in combination with immigration (the spreading of a new species from the site where it evolved out into different areas).
Evolution by common descent, as above, with God having set everything in motion in the beginning -- for instance, at the initial creation of the universe, or at the initial occurrence of life on earth -- and not having affected anything since.
Evolution by common descent, as above, with God occasionally altering the direction of evolution (e.g., causing sudden extinctions of certain groups, causing certain mutations to arise). The extent of the "tinkering" could vary from almost none to constant adjustments. However, a "constant tinkering" theory may run into the problem that vertebrate history on the whole does not show any obvious direction. For instance, mammal evolution does not seem to have led inescapably toward humans, and does not show any consistent discernable trend (except possibly toward increased body size). Many lineages do show some sort of trend over time, but those trends were usually linked to available ecological niches, not to an inherent "evolutionary path", and the "trends" often reversed themselves when the environment or the competition changed.
Models 1, 2, and 3 are all consistent with the known fossil record.
Creation of separate "kinds" in the order listed in Genesis, in six days, followed by a cataclysmic flood.
The Flood model is completely falsified, since the fossils appear in a different order than can be explained by any conceivable "sorting" model. Note that this is true not just for terrestrial vertebrates, but also for aquatic vertebrates, pollen, coral reefs, rooted trees, and small invertebrates. For example, ichthyosaurs and porpoises are never (not once!) found in the same layers; crabs and trilobites are never found in the same layers; small pterosaurs and equal-sized modern birds and bats are never found in the same layers. In addition, countless geological formations seem to be the result of eons of gradual accumulation of undisturbed sediment, such as multi-layer river channels and deep-sea sediments, and there are no indications of a single worldwide flood. In addition, the Flood Model cannot account for the obvious sorting by subtle anatomical details (easily explained by evolutionary models), or for the phenomenon that lower layers of lava have older radiometric dates. These are only a few of the problems with the Flood Model. See the flood FAQ for further information.
Creation in six "metaphorical" days is also falsified, since the animals appeared in a different order than that listed in Genesis, and over hundreds of millions of years rather than six days.
Literal creationism won't fly, but could the concept of "separately created kinds" still be viable, with the creations occurring over millions of years? This would require the following convoluted adjustments:
First, if every "kind", (species, genus, family, whatever) was separately created, there must have been innumerable successive and often simultaneous waves of creation, occurring across several hundred million years, including thousands of creations of now- extinct groups.
Second, these thousands of "kinds" were created in a strictly correlated chronological/morphological sequence, in a nested hierarchy. That is, virtually no "kind" was created until a similar "kind" already existed. For instance, for the reptile-to-mammal transition, God must have created at least 30 genera in nearly perfect morphological order, with the most reptilian first and the most mammalian last, and with only relatively slight morphological differences separating each successive genus. Similarly, God created legged whales before he created legless whales, and Archeopteryx before creating modern birds. He created small five-toed horse- like creatures before creating medium-sized three-toed horses, which in turn were created before larger one-toed horses. And so on. This very striking chronological/morphological sequence, easily explained by models 1, 2, and 3, is quite puzzling in this model.
Third, God did not create these kinds in a sequence that obviously progressed in any direction, as discussed briefly under model 3. This is not necessarily a fatal flaw (mysterious are the ways of God, right?), but it is another puzzle, another unexplained aspect of the fossil record.
Fourth, what about those species-to-species transitions? They appear to show that at least some species, genera, and families arose by evolution (not necessarily all, but at least some.) How can a creationist model be reconciled with this evidence?
In this model, the species-species transitions DO represent evolution, but of a minor and unimportant variety. Note, however, that during these bursts of "minor evolution", the evolution took place in an apparently non-directed manner, sometimes crossed genus and family lines, and resulted in just the same sorts of morphological differences that are seen between the other, presumably created, groups of animals.
In this model, the "species-species transitions" do not represent evolution. This implies that every individual fossil in the species-to-species transitions must have been separately created, either by creation of the animal that later died and was fossilized, or by creation of a fossil in situ in the rock. I have heard this model called the "Lying God Theory".
Okay, having blathered on about that, now I'll quit pontificating and get to the main point.
As Gould said (1994): "The supposed lack of intermediary forms in the fossil record remains the fundamental canard of current antievolutionists. Such transitional forms are scarce, to be sure, and for two sets of reasons - geological (the gappiness of the fossil record) and biological (the episodic nature of evolutionary change, including patterns of punctuated equilibrium and transition within small populations of limited geological extenet). But paleontologists have discovered several superb examples of intermediary forms and sequences, more than enough to convince any fair-minded skeptic about the reality of life's physical geneology."
Ahlberg, P.E. 1991. Tetrapod or near-tetrapod fossils from the Upper Devonian of Scotland. Nature 354:298-301.
Barnosky, A.D. 1987. Punctuated equilibrium and phyletic gradualism: some facts from the Quaternary mammalian record. Chapter 4, pp 109- 148, in: Current Mammalogy, volume 1, ed. H.H. Genowys. Plenum Press, New York.
Benton, M.J. (ed.) 1988. The Phylogeny and Classification of the Tetrapods. Clarendon Press, Oxford. [collection of papers. Good intro to current thinking on many intermediate fossils from various groups.]
Benton, M.J. 1989. Patterns of evolution and extinction in vertebrates. Pp 218-241 in: Evolution and the Fossil Record, eds. K. Allen & D. Briggs. Smithsonian Institution Press, Washington, D.C.
Benton, M.J. 1990. Vertebrate Palaeontology: biology and evolution. Unwin Hyman, London.
Berta, A. 1994. What is a whale? Science 263:180-181. [commentary on discovery of Ambulocetus natans]
Bolt, J.R., R.M. McKay, B.J. Witzke, & M.P. Adams. 1988. A new Lower Carboniferous tetrapod locality in Iowa. Nature 333:768-770
Carroll, R. 1988. Vertebrate Paleontology and Evolution. W.H. Freeman & Co., New York. [general text. Only chapter 22 is concerned with species-level evolution and transitions; the other chapters generally describe only genera or families.]
Chaline, J. 1983. Modalites, Rythmes, Mecanismes de L'Evolution Biologique: Gradualisme phyletique ou equilibres ponctues? Editions du Centre National de la Recherche Scientifique, Paris. [collection of symposium papers, most in French with English abstracts provided, some in English.]
Chaline, J., and B. Laurin. 1986. Phyletic gradualism in a European Plio-Pleistocene Mimomys lineage (Arvicolidae, Rodentia). Paleobiology 12:203-216.
Chevret, P., C. Denys, J.J. Jaeger, J. Michaux, and F. Catzeflis. 1993. Molecular and paleontological aspects of the tempo and mode of evolution in Otomys (Otomyinae: Muridae: Mammalia). Biochem. Syst. Ecol. 21(1):123-131.
Chuankuei-Li, R.W. Wilson, M.R. Dawson, and L. Krishtalka. 1987. The origin of rodents and lagomorphs. Chapter 3, pp. 97-108, in: Current Mammalogy, volume 1, ed. HH Genoways. Plenum Press, New York.
Coates, M.I., & J.A. Clack. 1991. Fish-like gills and breathing in the earliest known tetrapod. Nature 352:234-236.
Coates, M.I., & J.A. Clack. 1990. Polydactyly in the earliest known tetrapod limbs. Nature 347:66-69.
Colbert, E.H. & M. Morales. 1991. Evolution Of The Vertebrates: A History Of The Backboned Animals Through Time. Wiley-Liss, New York. [An accessible summary of large-scale trends in vertebrate history. Does not discuss species-level evolution at all, though.]
Daeschler, E.B., N.H. Shubin, K.S. Thomson, W.W. Amaral. 1994. A Devonian tetrapod from North America. Science 265:639-642.
Edwards, J.L. 1989. Two perspectives on the evolution of the tetrapod limb. Am. Zool. 29:235-254.
Fahlbusch, V. 1983. Makroevolution. Punktualismus. Ein Diskussionsbeitrag am Beispiel miozaner Eomyiden (Mammalia, Rodentia). Palaont. Z. 57:213-230. [transitions among Miocene rodents.]
Feduccia, A. 1980. The Age Of Birds. Harvard University Press, Cambridge, Mass.
Fischman, J. 1993. Paleontologists examine old bones and new interpretations. Science 262: 845-846.
Futuyma, D.J. 1982. Science on Trial: The Case for Evolution. Pantheon Books, New York.
Futuyma, D.J. 1986. Evolutionary Biology. Sinauer Associates, Sunderland, Mass. [standard text on theories of how evolution occurs; doesn't address evidence for evolution per se].
Gingerich, P.D. 1976. Paleontology and phylogeny: Patterns of evolution at the species level in early Tertiary mammals. Am. J. Sci. 276:1-28.
Gingerich, P.D. 1977. Patterns of evolution in the mammalian fossil record. In: Patterns Of Evolution As Illustrated By The Fossil Record (ed. A. Hallam), chapter 15, pp. 469-500. Elsevier Scientific Pub. Co.
Gingerich, P.D. 1980. Evolutionary patterns in early Cenozoic mammals. Ann. Rev. Earth Planet. Sci. 8:407-424.
Gingerich, P.D. 1982. Time resolution in mammalian evolution: Sampling, lineages, and faunal turnover. Third North Am. Paleont. Conv., Proc., 1:205-210.
Gingerich, P.D. 1983. Evidence for evolution from the vertebrate fossil record. J. Geological Education 31:140-144.
Gingerich, P.D. 1985. Species in the fossil record: concepts, trends, and transitions. Paleobiology 11(1):27-41.
Gingerich, P.D., B.H. Smith, & E.L. Simons. 1990. Hind limb of Eocene Basilosaurus: evidence of feet in whales. Science 249:154-156.
Gould, S.J. 1983. Hen's Teeth And Horse's Toes. W.W. Norton, New York. [The title essay discusses evidence that some species retain old genes for traits that they no longer express -- teeth in chickens, side toes in horses. ]
Gould, S.J. 1993. Eight Little Piggies. W.W. Norton, New York. [collection of essays. Title essay is about early amphibians.]
Gould, S.J. 1994. Hooking Leviathon by its past. Natural History, May 1994.
Harris, J., & White, T.D. 1979. Evolution of Plio-Pleistocene African Suidae. Trans. Am. Phil. Soc. 69:1-128.
Hopson, J.A. 1991. Convergence in mammals, tritheledonts, and tridylodonts. J. Vert. Paleont. 11(suppl. to 3):36A [abstract]
Horner, J.R., D.J. Varrichio, and M.B. Goodwin. 1992. Marine transgressions and the evolution of Cretaceous dinosaurs. Nature 358:59-61.
Hurzeler, J. 1962. Kann die biologische Evolution, wie sie sich in der Vergangengeit abgespielt hat, exakt erfasst werden? Stud. Kath. Akad. Bayern. 16:15-36.
Kemp, T.S. 1982. Mammal-like reptiles and the origin of mammals. Academic Press, New York.
Kermack, D.M. & Kermack, K.A. 1984. The evolution of mammalian characters. Croom Helm Kapitan Szabo Publishers, London. [this is a great little book; very clearly written, short, and well- illustrated.]
Krishtalka, L., and Stucky, R.K. 1985. Revision of the Wind River Faunas. Early Eocene of Central Wyoming. Part 7. Revision of Diacodexis (Mammalia, Artiodactyla). Am. Carnegie Mus. 54:413-486.
Kurten, B. 1964. The evolution of the polar bear, Ursus maritimus (Phipps). Acta Zoologica Fennica 108:1-26.
Kurten, B. 1968. Pleistocene Mammals of Europe. Aldine, Chicago.
Kurten, B. 1976. The Cave Bear Story. Columbia University Press, New York.
Laurin, M. 1991. The osteology of a Lower Permian eosuchian from Texas and a review of diapsid phylogeny. Zool. J. Linn. Soc. 101:59-95.
Lee, M.S.Y. 1993. The origin of the turtle bodyplan: bridging a famous morphological gap. Science 261:1716-1720.
Lucas, S.G., and Z. Lou. 1993. Adelobasileus from the upper Triassic of west Texas: the oldest mammal. J. Vert. Paleont. 13(3):309-334.
Lundelius, E.L., T. Downs, E.H. Lindsay, H.A. Semken., R.J. Zakrzewski, C.S. Churcher, C.R. Harington, G.E. Schultz, and S.D. Webb. 1987. The North American Quaternary sequence. In: Cenozoic Mammals of North America - Geochronology and Biostratigraphy (ed. M.O. Woodburne). University of California Press, Berkeley.
MacFadden, B.J. 1985. Patterns of phylogeny and rates of evolution in fossil horses: Hipparions from the Miocene and Pliocene of North America. Paleobiology 11:245-257.
MacFadden, B.J. 1988. Horses, the fossil record, and evolution: a current perspective. Evol. Biol. 22:131-158.
MacFadden, B.J., & R.C. Hubbert. 1988. Explosive speciation at the base of the adaptive radiation of Miocene grazing horses. Nature 336:466-468. (An interesting summary of the merychippine radiation. Has a nice horse tree, too. MacFadden's horse tree is used by almost everyone these days.)
MacFadden, B.J., J.D. Bryant, and P.A. Mueller. 1991. Sr-isotopic, paleomagnetic, and biostratigraphic evidence of horse evolution: evidence from the Miocene of Florida. Geology 19:242-245. [This is an interesting example of the variety of dating methods paleontologists use to date their finds. MacFadden et al. dated the Parahippus --> Merychippus transition at a Florida site with paleomagnetic data and Sr/Sr dates, and also by cross-correlation to other sites dated with Sr/Sr, K/Ar, Ar/Ar, zircon fission-track, and paleomagnetic dating methods. All the dates were consistent at roughly 16 Ma.]
Maglio, V.J. 1973. Origin and evolution of the Elephantidae. Trans. Am. Phil. Soc., New Ser. 63:1-149.
Martin, R.A., and A.D. Barnosky, eds. 1993. Morphological Change in Quaternary Mammals of North America. Cambridge University Press, New York. [collection of papers. Particulary useful: Goodwin on prairie dogs, Hulbert & Morgan on armadillos, Lister on mammoths and moose, Martin on rodents.]
Milner, A.R., and S.E. Evans. 1991. The Upper Jurassic diapsid Lisboasaurus estesi -- a maniraptoran theropod. Paleontology 34:503-513.
Prothero, D.R., & R.M. Schoch, eds. 1989. The Evolution of Perissodactyls. Clarendon Press, New York. [collection of papers]
Rayner, M.J. 1989. Vertebrate flight and the origins of flying vertebrates. Pp. 188-217 in: Evolution and the Fossil Record, eds. K. Allen & D. Briggs. Smithsonian Institution Press, Washington, D.C.
Reisz, R., & Laurin, M. 1991. Owenetta and the origin of the turtles. Nature 349: 324-326.
Reisz, R., & Laurin, M. 1993. The origin of turtles. J. Vert. Paleont. 13 (suppl. 3):46 [abstract]
Rensberger, J.M. 1981. Evolution in a late Oligocene-early Miocene succession of meniscomyine rodents in the Deep River Formation, Montana. J. Vert. Paleont. 1(2): 185-209.
Rose, K.D., and Bown, T.M. 1984. Gradual phyletic evolution at the generic level in early Eocene omomyid primates. Nature 309:250-252.
Rowe, T. 1988. Definition, diagnosis, and origin of Mammalia. J. Vert. Paleont. 8(3): 241-264.
Rougier, G.W., J.R. Wible, and J.A. Hopson. 1992. Reconstruction of the cranial vessels in the early Cretaceous mammal Vincelestes neuquenianus: implications for the evolution of the mammalian cranial vascular system. J. Vert. Paleont. 12(2):188-216.
Sanz, J.L., Bonaparte, J.F., and A. Lacassa. 1988. Unusual Early Cretaceous birds from Spain. Nature 331:433-435. [This is about the Las Hoyas bird. ]
Sanz, J.L and Bonaparte, J.F. 1992. A new order of birds (Class Aves) from the lower Cretaceous of Spain. in K.E.Campbell (ed.) Papers in Avian Paleontology. Natural History Museum of Los Angeles County, Science Series No.36 [Formal description of the Las Hoyas bird.]
Sereno, P.C. and Rao, C. 1992. Early evolution of avian flight and perching: new evidence from the lower Cretaceous of China. Science vol.255, pp.845-848.
Shubin, N.H., A.W. Crompton, H.-D. Sues, P.E. Olsen. 1991. New fossil evidence on the sister-group of mammals and early Mesozoic faunal distribution. Science 251:1063-1065.
Simpson, G.G. 1961. Horses. Doubleday & Co., New York. [outdated but still the most accessible intro to horse evolution.]
Szalay, F.S., M.J. Novacek, and M.C. McKenna. 1993. Mammal Phylogeny, vols 1 & 2. Springer-Verlag, New York. [a compilation of articles on different groups of mammals. Volume 1 covers early Mesozoic mammals, monotremes, and marsupials, volume 2 covers Cenozoic placentals. Excellent intro to the current state of knowledge of mammal relationships, though to get the most from it you should be familiar with current phylogenetic methodology and vertebrate morphology.]
Thewissen, J.G.M., S.T. Hussain, and M. Arif. 1993. Fossil evidence for the origin of aquatic locomotion in archaeocete whales. Science 263:210-212.
Wellnhofer, P. 1993. Das siebte Exemplar von Archaeopteryx aus den Solnhofener Schichten. Archaeopteryx vol.11, pp. 1-47. [Description of the newest specimen of Archaeopteryx, with some more features that unite birds with dinosaurs. Summary and all figure legends are in English, the rest is in German.]
Werdelin, L, and N Solounias. 1991. The Hyaenidae: taxonomy, systematics, and evolution. Fossils and Strata 30 (a monograph). Universitetsforlaget, Oslo.
White, T.D., G. Suwa, and B. Asfaq. 1994. Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopida. Nature 371:306- 312.
Wible, J.R. 1991. Origin of Mammalia: the craniodental evidence reexamined. J. Vert. Paleont. 11(1):1-28.
Wood, B.A. 1994. The oldest hominid yet. Nature 371:280-281. [commentary on Australopithecus ramidus]
MAGAZINE ARTICLES by unknown authors:
Science News 133:102. "Bird fossil reveals history of flight".
Science News 145(3):36. "Fossil Whale Feet: A Step in Evolution" [Ambulocetus natans & other recent whale discoveries]
Science News 140:104-105. 1991. "The Lonely Bird." [summary of the Protoavis controversy.]
Science News 138:246-247. 1990. "Chinese bird fossil: mix of old and new".
Discover, (month?) 1991. Article on Protoavis.
Discover, January 1995. "Back to the Sea". Brief description of recent fossil whale discoveries, with a nice full-color painting depicting evolution to the sea (showing a mesonychid on land, Ambulocetus at the shoreline, the legged Eocene whale Rodhocetus in shallow water, and the later vestigial-legged whale Prozeuglodon in deep water.)
Discover, February 1995, p. 22 "Wabbit or Wodent?" Brief description, with photo, of a probably rodent/lagomorph ancestor.
Warren Kurt von Roeschlaub
...and anyone else I've forgotten!
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