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Icons of ? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Education DARWIN’S “ OF ” mon descent. Finally, he demands that text- books treat universal common ancestry as PHYLOGENETIC unproven and refrain from illustrating that n , a , or phyloge- “theory” with misleading phylogenies. ny, is used to show the genealogic relation- Therefore, according to Wells, textbooks Iships of living things. A phylogeny is not should state that there is no evidence for com- so much evidence for evolution as much as it mon descent and that the most recent research is a codification of data about evolutionary his- refutes the concept entirely. Wells is complete- tory. According to biological evolution, - ly wrong on all counts, and his argument is isms share common ; a phylogeny entirely based on misdirection and confusion. shows how are related. The tree of He mixes up these various topics in to life shows the path evolution took to get to the confuse the reader into thinking that when current diversity of life. It also shows that we combined, they show an endemic failure of can ascertain the genealogy of disparate living evolutionary theory. In effect, Wells plays the organisms. This is evidence for evolution only equivalent of an intellectual shell game, put- in that we can construct such trees at all. If ting so many topics into play that the “ball” of evolution had not happened or common ances- evolution gets lost. try were false, we would not be able to discov- THE EXPLOSION er hierarchical branching genealogies for ells claims that the Cambrian organisms (although textbooks do not general- Explosion “presents a serious chal- ly explain this well). Referring to any phylo- lenge to Darwinian evolution” genetic tree as “Darwin’s ” is some- W (Wells, 2000:41) and the validity of phyloge- what of a misnomer. Darwin graphically pre- netic trees. The gist of Wells’s argument is that sented no phylogenies in the Origin of ; the happened too fast to the only figure there depicts differential rates allow large-scale morphological evolution to of . If anyone deserves credit for occur by (“”), and giving us “trees of life,” it is , that the Cambrian Explosion shows “top- who drew phylogenies for many of the living down” origination of taxa (“major” “phyla” groups of literally as trees, as well as level differences appear early in the coining the term itself. record rather than develop gradually), which WELLS’S SHELL GAME he claims is the opposite of what evolution ells uses phylogenetic trees to attack predicts. He asserts that phylogenetic trees the very core of evolution — com- predict a different pattern for evolution than Wmon descent. Wells claims that text- what we see in the Cambrian Explosion. These books mislead students about arguments are spurious and show his lack of in three ways. First, Wells claims that text- understanding of basic aspects of both paleon- books do not cover the “Cambrian Explosion” tology and evolution. and fail to point out how this “top-down” pat- Wells mistakenly presents the Cambrian tern poses a serious challenge to common Explosion as if it were a single event. The descent and evolution. Second, he asserts that Cambrian Explosion is, rather, the preserva- the occasional disparity between morphologi- tion of a of that occur over a 15– cal and molecular phylogenies disproves com- 20 million period starting around 535 mil- 11 ? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education ago (MA). A is a group of claiming that this proves that the fossil record organisms that live together and interact as an is complete enough to show that there were no ; in , “fauna” refers to a precursors for the Cambrian Explosion ani- group of organisms that are fossilized together mals. This claim is false. His evidence for this because they lived together. The first fauna “well documented” fossil record that shows extensive diversity is the is a selective quote from the final sentence in Sirius Passet fauna of , which is an article by Benton et al. (2000). While the dated at around 535 MA (Conway Morris, paper’s final sentence does literally say that 2000). The organisms preserved become more the “early” parts of the fossil record are ade- diverse by around 530 MA, as the Chenjiang quate for studying the patterns of life, Wells fauna of illustrates (Conway Morris, out a critical detail: the sentence refers 2000). Wells erroneously claims that the not to the Precambrian, but to the Cambrian Chenjiang fauna predates the Sirius Passet and later . Even more ironic is the fact (Wells, 2000:39). The diversification contin- that the conclusion of the paper directly refutes ues through the Burgess fauna of Canada Wells’s claim that the fossil record does not at around 520 MA, when the Cambrian faunas support the “tree of life.” Benton et al. (2000) are at their peak (Conway Morris, 2000). Wells assessed the completeness of the fossil record makes an even more important paleontological using both molecular and morphological error when he does not explain that the “explo- analyses of phylogeny. They showed that the sion” of the late Early and Middle Cambrian is sequence of appearance of major taxa in the preceded by the less diverse “small shelly” fossil record is consistent with the pattern of metazoan faunas, which appear at the begin- phylogenetic relationships of the same taxa. ning of the Cambrian (545 MA). These faunas Thus they concluded that the fossil record is are dated to the early Cambrian, not the consistent with the tree of life, entirely oppo- Precambrian as stated by Wells (Wells, site to how Wells uses their paper. 2000:38). This enables Wells to omit the Wells further asserts that there is no evi- steady rise in fossil diversity over the ten mil- dence for metazoan life until “just before” the lion years between the beginning of the Cambrian explosion, thereby denying the nec- Cambrian and the Cambrian Explosion (Knoll essary for evolution to occur. Yet Wells is and Carroll, 1999). evasive about what counts as “just before” the In his attempt to make the Cambrian Cambrian. Cnidarian and possible Explosion seem instantaneous, Wells also embryos are present 30 million years “just grossly mischaracterizes the Precambrian fos- before” the Cambrian (Xiao et al., 1998). sil record. In order to argue that there was not There is also a mollusc, , from the enough time for the necessary evolution to White of Russia (Fedonkin and Waggoner, occur, Wells implies that there are no in 1997) dated approximately 555 million years the Precambrian record that suggest the com- ago, or 10 million years “just before” the ing diversity or provide evidence of more Cambrian (Martin et al., 2000). This primitive primitive multicellular animals than those seen has an uncalcified “shell,” a muscular in the Cambrian Explosion (Wells, 2000:42– foot (Fedonkin and Waggoner, 1997), and a 45). He does this not by producing original radula inferred from “mat-scratching” feeding research, but by selectively quoting paleonto- patterns surrounding fossilized individuals logical literature on the fossil record and (personal observation; Seilacher, pers. 12 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education comm.). These features enable us to recognize Cambrian Explosion, for example, is the first it as a primitive relative of molluscs, even time we are able to distinguish a from though it lacks a calcified shell. There are also an arthropod. This does not mean that the chor- Precambrian (Gehling and Rigby, date or arthropod lineages evolved then, only 1996) as well as numerous trace fossils indi- that they then became recognizable as such. cating burrowing by wormlike metazoans For a simple example, consider the . How beneath the surface of the ’s floor do you know a turtle is a turtle? By the shell. (Seilacher, 1994; Fedonkin, 1994). Trace fos- How would you recognize the ancestors of the sils demonstrate the presence of at least one living turtle, before they evolved the shell? ancestral lineage of bilateral animals nearly 60 That is more complicated. Because its ances- million years “just” before the Cambrian tors would have lacked the diagnostic feature (Valentine et al., 1999). Sixty million years is of a shell, ancestral may be hard to rec- approximately the same amount of time that ognize (Lee, 1993). In order to locate the has elapsed since the of non-avian remote ancestors of turtles, other, more subtle, , providing plenty of time for evolu- features must be found. tion. In treating the Cambrian Explosion as a Similarly, before the Cambrian Explosion, single event preceded by nothing, Wells mis- there were lots of “,” now preserved as represents fact — the Cambrian explosion is trace fossils (i.e., there is evidence of burrow- not a single event, nor is it instantaneous and ing in the sediments). However, we cannot dis- lacking in any precursors. tinguish the chordate “worms” from the mol- Continuing to move the shells, Wells lusc “worms” from the arthropod “worms” invokes a semantic sleight of hand in resur- from the “worms.” Evolution predicts recting a “top-down” explanation for the diver- that the of all these groups was worm- sity of the Cambrian faunas, implying that like, but which worm evolved the , phyla appear first in the fossil record, before and which the jointed appendages? In his argu- lower categories. However, his argument is an ment, Wells confuses the identity of the indi- artifact of taxonomic practice, not real mor- vidual with how we diagnose that identity, a phology. In traditional , the recogni- failure of logic that dogs his discussion of tion of a species implies a . This is due in the following chapter. If the ani- to the rules of the taxonomy, which state that if mal does not have the typical diagnostic fea- you find a new , you have to assign it tures of a known phylum, then we would be to all the necessary taxonomic ranks. Thus unable to place it and (by the rules of taxono- when a new organism is found, either it has to my) we would probably have to erect a new be placed into an existing phylum or a new one phylum for it. When paleontologists talk about has to be erected for it. Cambrian organisms the “sudden” origin of major animal “body are either assigned to existing “phyla” or new plans,” what is “sudden” is not the appearance ones are erected for them, thereby creating the of animals with a particular body plan, but the effect of a “top-down” emergence of taxa. appearance of animals that we can recognize as Another reason why the “higher” taxonom- having a particular body plan. Overall, howev- ic groups appear at the Cambrian Explosion is er, the fossil record fits the pattern of evolu- because the Cambrian Explosion organisms tion: we see evidence for worm-like bodies are often the first to show features that allow first, followed by variations on the worm us to relate them to living groups. The theme. Wells seems to ignore a growing body 13 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education

Figure 3. Stepwise evolution of features as illustrated by living and fossil animals. of literature showing that there are indeed cally worms with a stiff rod (the notochord) in organisms of intermediate morphology present them. The amount of change between a worm in the Cambrian record and that the classic and a worm with a stiff rod is relatively small, “phyla” distinctions are becoming blurred by but the presence of a notochord is a major fossil evidence (Budd, 1998, 1999; Budd and “body-plan” distinction of a chordate. Further, Jensen, 2000). it is just another small step from a worm with Finally, the “top-down” appearance of a stiff rod to a worm with a stiff rod and a head body-plans is, contrary to Wells, compatible (e.g., Haikouella; Chen et al., 1999) or a worm with the predictions of evolution. The issue to with a segmented stiff rod (vertebrae), a head, be considered is the practical one that “large- and fin folds (e.g., Haikouichthyes; Shu et al., scale” body-plan change would of course 1999). Finally add a fusiform body, fin differ- evolve before minor ones. (How can you vary entiation, and scales: the result is something the lengths of the before you have a resembling a “” (Figure 3). But, as soon as head?) The difference is that, many of the the stiff rod evolved, the animal was suddenly “major changes” in the Cambrian were initial- no longer just a worm but a chordate — repre- ly minor ones. Through time they became sentative of a whole new phylum! Thus these highly significant and the basis for “body- “major” changes are really minor in the begin- plans.” For example, the most primitive living ning, which is the Precambrian–Cambrian chordate Amphioxus is very similar to the period with which we are concerned. Cambrian fossil chordate Pikia. Both are basi- 14 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education

CONGRUENCE OF PHYLOGENIES BASED ON DIFFERENT SOURCES OF DATA ells also points to the occasional lack of congruence between molec- Wular- and morphology-based phylo- genies as evidence against common descent. (Molecular phylogenies are based on compar- isons of the of organisms.) Wells omits the fact that the discrepancies are frequently small, and their causes are largely understood (Patterson et al., 1993; Novacek, 1994). Although not all of these discrepancies can yet be corrected for, most genetic and morpholog- ical phylogenies are congruent for 90% of the Figure 4. relationships based on taxa included. For example, all phylogenies, different sources of data. Note that the only whether morphological or molecular, consider group whose position varies is turtles. all animals bearing amniotic to be more closely related to one another than to amphib- a few possibilities (Rieppel and deBraga, ians. Within this group, all reptiles and 1996; Lee, 1997; deBraga and Rieppel, 1997; are more closely related to each other than they Zardoya and Meyer, 1998; Rieppel and Reiz, are to . Finally, birds and crocodiles 1999; Rieppel, 2000; Figure 4), and none of are more closely related to each other than to these claim turtles are mammals. The uncer- , , and the tuatara (Gauthier et al., tainty over the precise placement of turtles 1988; Gauthier, 1994). The only group whose with respect to other groups, however, does not placement varies for both molecular and mor- mean that they did not evolve. Unfortunately, phology data sets is turtles. This is due to a genes can never be totally compared to mor- phenomenon called “long branch attraction” or phology since genetic trees cannot take fossil the “Felsenstein Zone” (Huelsenbeck and taxa into account: genes don’t fossilize. No Hillis, 1993). Long branch attraction is caused diagnostic tool of science is perfect. The when a organism has had so much evolution- imperfections in phylogenetic reconstruction ary change that it cannot be easily compared to do not make common ancestry false. Besides, other organisms, and due to the of the are these extremely technical topics really methodology used to evaluate phylogeny, it appropriate for introductory textbooks? can appear to be related to many possible Instead of clearly discussing these actual organisms (Felsenstein, 1978; Huelsenbeck phylogenetic issues, Wells invents one that and Hillis, 1993). This is the case for turtles. isn’t even real. He cites a 1998 paper that Turtles are so morphologically and genetically placed cows phylogenetically closer to whales different from the rest of the reptiles that they than to horses, calling that finding “bizarre” are hard to place phylogenetically (Zardoya (Wells, 2000:51). Yet this is not “bizarre” at and Meyer, 2001). Still, researchers have nar- all; it was expected. All the paleontological rowed down the possible turtle relationships to and molecular evidence points to a whale 15 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education orgin within artiodactyls, and further to the THE UNIVERSAL COMMON fact that artiodactyls (cows, deer, antelopes, ANCESTOR pigs, etc.) are not more closely related to peris- inally, Wells cites the “failure” of molec- sodactyls (horses, rhinos, and the tapir) than ular phylogeny to clarify the position of they are to whales (Novacek, 1992, 2001). Fthe Universal Common Ancestor as Wells makes this statement smugly, as if to proof that there is no common ancestry for any suggest that everyone should think that this of life. Here, Wells mixes up the different sounds silly. Unfortunately, it is Wells’s criti- scales of descent in order to tangle the reader cism that is silly. in a thicket of phylogenetic branches. He is

Figure 5. The traditional view of phylogenetic relationships for the three “domains” of life com- pared to Woese’s view. Note that the only difference lies in whether there is a single “root” at the base of the tree. Regardless, , archaeans, and all share a common ancestor on both, although Woese does posit a greater degree of lateral trasfer for single-celled organisms. 16 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education attacking the notion that life originated with pods, or angiosperms (Figure 5). That is still a one population, and that all life can trace its lot of evolution that Wells’s inaccurate attack ancestry back to that population, the Universal on the idea of a UCA does nothing to dispel. Common Ancestor (UCA). The problem has WHAT THE TEXTBOOKS SAY been that it is hard to determine relationships when there is nothing to compare to. How do he concept of common ancestry is at the you compare “not life” to “life”? We have no core of evolution. The very idea that fossils of the earliest forms of life, and the high Tdifferent species arise from previous degree of genetic change that has occurred in forms via descent implies that all living things the 3.8 billion years since the early stages of share a common ancestral population at some life make it nearly impossible to reconstruct point in their history. This concept is support- the “original” . This does not ed by the fossil record, which shows a history invalidate the concept of common ancestry; it of lineages changing through time. Because just makes it difficult and potentially impossi- evolution is the basis for biology, it would be ble to untangle the lineages. And this does not surprising if any textbook teaching contempo- mean that there is not one real lineage: the rary biology would portray common descent inability to determine the actual arrangement other than -of-factly. of “domains” at the base of the tree or to char- Textbooks treat the concept of common acterize the UCA does not make the UCA any descent in basically the same way as do scien- less real than the inability to characterize light tists; they accept common ancestry of living unambiguously as either a wave or a things as a starting point, and proceed from makes light unreal. there. Phylogenies thus appear in many places Some authors (e.g., Woese, 1998) go further in a text, which makes it very hard to evaluate and suggest that there is no “UCA”; rather, exactly how textbooks “misrepresent” biologi- they suggest, life arose in a soup of competing cal evolution using trees. Most texts show a . These genomes were constantly phylogeny in chapters discussing exchanging and mixing, and thus cellular life and taxonomy. In this there is usually a may have arisen multiple times. Wells misrep- tree of “” or “” relationships, resents the statements of those scientists to which may be what Wells considers a tree make it look as if they are questioning the showing “universal” common ancestry; unfor- entirety of common ancestry, when what they tunately, his discussion is too vague for a read- question is just the idea of a single common er to be sure whether that is what he is refer- ancestor at the base of life. Further, when some ring to. Many textbooks show additional, more suggest that we should abandon the search for detailed trees in their discussions of different the UCA, they do not mean that they don’t taxonomic groups. In terms of textbook pre- think it existed. They mean only that it may be sentations, then, there is no single “Darwin’s a waste of time to try to find it given the cur- tree of life” presented in some iconic state, but rent technology and methods at our disposal. many various phylogenies shown in the appro- Regardless of the status of a UCA, which is at priate sections of most books. Textbooks also the base of the tree of life, the entire debate has present trees in the chapters on processes and nothing to do with the branches of the tree — mechanisms of evolution, in the “Origin of the shared descent of eukaryotes, of animals, life” or “” chapters, and in chap- or common descent among , arthro- ters dealing with individual taxonomic groups. 17 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education

Figure 6. Evaluation of Wells’s grading of Textbook Icon #2, “Darwin’s Tree of Life.” Parenthetical notations indicate the number of phylogenetic trees shown in the book.

18 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education This is because phylogenetic trees are not part “explosion.” These discussions usually men- of the “evidence for evolution,” but rather tion that it was a “rapid” origin of animal graphical representations of the history, groups. Does Wells actually require that the genealogy, and taxonomy of life. No textbook book explicitly mention the “Cambrian misrepresents the methods that are used to Explosion” by name? If so, it should have been construct trees or the trees themselves, specified in the criteria. Or is it that it he only although some trees contain out-of-date rela- looked for “Cambrian Explosion” in the noto- tionships and occasionally incorrect identifica- riously spotty indexes of the textbooks? A tions of organisms pictured in them. When reevaluation suggests that five of the books to textbooks cover the Cambrian period, the rapid which he gives an F should receive, even by appearance of many body plans is discussed his criteria, a D. Finally, one text (Miller and not as a “paradox” for evolutionary theory, but Levine’s) even mentions the confusing nature as an interesting event in the history of life — of the basal divergence of life caused by later- which is how paleontologists and evolutionary al transfer, yet this discussion can receive no consider it. credit in the grading. This is because although WELLS’SEVALUATION Wells considers the “phylogenetic thicket” to be extremely important to reject universal verall, Wells’s grading system for this common ancestry, he apparently does not con- “icon” is so nebulous that it is hard to sider it important enough to account for it in Ofigure out exactly how he evaluated his grading scheme. All of this calls into ques- the textbooks at all. The “Universal Common tion how well Wells actually reviewed the texts Ancestor” is far different from the “Cambrian he graded as well as whether his grades have Explosion.” These deal with very different any utility at all. places in the “tree of life” as well as very dif- ferent issues in evolution. Wells’s grades seem WHY WE SHOULD CONTINUE TO largely based on presentations of “common TEACH COMMON DESCENT ancestry.” For example, according to Wells, if here is no reason for textbooks to sig- the textbook treats common ancestry as “fact,” nificantly alter their presentations of then it can do no better than a D. In order to get Tcommon descent or phylogenetic trees. a C or better, a book must also discuss the As long as biological evolution is the paradigm “top-down” nature of the Cambrian explosion of biology, common descent should be taught. as a “problem” for evolution; if a book only All living organisms that reproduce have off- mentions the Cambrian Explosion, it gets a D. spring that appear similar to, but not exactly Here Wells does not even apply his grading like, their parents. We can observe descent scheme consistently (Figure 6). For example, with modification every day, and like Darwin, Wells chastises textbooks (Miller and Levine’s we can confidently extrapolate that it has gone in particular) for not discussing the Cambrian on throughout the history of life. Through this Explosion, yet most of the textbooks he process, small differences would accumulate reviews actually mention it (Figure 6) and to larger differences and result in the evolution Miller and Levine devote an entire page (p. of diversity that we see today and throughout 601) to it. Many of the reviewed textbooks dis- the history of life. cuss the Cambrian period in the history of life The concept of descent allows us to make sections, but do not specifically call it an testable predictions about the fossil record and 19 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education the of organisms. For example, we Budd, G. E. 1998. Arthropod body-plan evolution in the predict that all animals sharing a common Cambrian with an example from anomalocarid muscle. ancestor would have a similar genetic code, Lethaia 31:197–210. use the same cellular processes, and so on; Budd, G. E., 1999. Does evolution in body patterning genes drive morphological change –– or vice versa? these predictions are confirmed by biochem- Bioessays 21:326–332. istry and genetics. In terms of fossils, we Budd, G. E. and S. Jensen. 2000. A critical reappraisal would expect to see animals with transitional of the fossil record of the bilaterian phyla. Biological morphologies in the past, as well as animals Reviews 75:253–295. that appear similar, but not identical, to those Chen, J.-Y., D.-Y. Huang, and C.-W. Li. 1999. An early living today. We also predict that these organ- Cambrian -like chordate. Nature 402:518–522. isms, both past and present, can be arranged Conway Morris, S. 2000. The Cambrian “explosion”: into a branching hierarchy of forms, which slow fuse or megatonnage? Proceedings of the National appears much like a genealogy. This is what Academy of Science 97:4429–4439. the biological considers science; DeBraga, M., and O. Rieppel. 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal this is what we should teach. of the Linnean Society 120:281–354. HOW TEXTBOOKS COULD IMPROVE Eernisse, and A. G. Kluge. 1993. Taxonomic congru- THEIR PRESENTATIONS ence versus total evidence, and amniote phylogeny OF PHYLOGENY inferred from fossils, molecules, and morphology. and Evolution 10:1170–1195. here is always room for improvement in Fedonkin, M. A., 1994. Vendian body fossils and trace the presentations of the concept of com- fossils. In S. Bengston, ed. Early Life on . Nobel Tmon descent. Textbooks could improve Symposium no. 84. Columbia University Press, New by updating the phylogenies, many of which York. p. 370–388. are now out-of-date. They should also remove Fedonkin, M. A., and B. M. Waggoner. 1997. The Late discussions of “phenetics” (an outdated Precambrian fossil Kimberella is a mollusc-like bilater- of phylogenetic reconstruction and classifica- ian organism. Nature 388:868–871. tion) from the phylogenetic reconstruction sec- Felsenstein, J. 1978. Cases in which parsimony or com- patibility methods will be positively misleading. tions, and expand discussions of and Systematic 27:401–410. more modern descent-based taxonomies. Gehling, J. G., and J. K. Rigby. 1996. Long expected Finally, textbooks should make a clear distinc- sponges from the Ediacara fauna of tion between molecular clocks and genetic South . Journal of Paleontology 70:185–195. phylogenies, something many fail to do clear- Gauthier, J. A., 1994. The diversification of the ly. However, to make textbooks conform to . In D. R. Prothero and R. M. Schoch eds. Wells’s criteria would be to misrepresent the Major Features of Vertebrate Evolution. Paleontological entire life sciences and to deprive students of Society Short Courses in Paleontology 7:129–159. pedagogically useful visual representations of Gauthier, J. A., A. G. Kluge, and T. Rowe. 1988. Amniote phylogeny and the importance of fossils. the unity of life. Cladistics 4:105–209. Huelsenbeck, J. P., and D. M. Hillis, 1993. Success of References phylogenetic methods in the four- case. Systematic Benton, M. J., M. A. Wills, and R. Hitchin. 2000. Biology 42:247–264. Quality of the fossil record through time. Nature Knoll, A. H., and S. B. Carroll. 1999. Early animal evo- 403:534–537. lution: emerging views from comparative biology and . Science 284:2129–2137. 20 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education

Lee, M. S. Y., 1993. The origin of the turtle body Woese, C. R. 1998. The universal common ancestor. plan:bridging a famous morphological gap. Science Proceedings of the National Academy of Science 261:1716–1720. 95:6854–6859. Lee, M. S. Y. 1997. Pareiasaur phylogeny and the origin Xiao, S., Y. Zhang, and A. H. Knoll. 1998. Three-dimen- of turtles. Zoological Journal of the Linnean Society sional preservation of and animal embryos in a 120:197–280. Neoproterozoic phosphorite. Nature 391:553–558. Martin, M. W., D. V. Grazhdankin, S. A. Bowring, D. A. Zardoya, R. and A. Meyer. 1998. Complete mitochondr- D. Evans, M. A. Fedonkin, and J. L. Kirschvink. 2000. ial suggests affinities of turtles. Age of Neoproterozoic Bilatarian body and trace fossils, Proceedings of the National Academy of Science White Sea, Russia: implications for metazoan evolution. 95:14226–14231. Science 288:841–845. Zardoya, R., and A. Meyer. 2001. The evolutionary Novacek, M. J. 1992. Mammalian phylogeny: shaking position of turtles revised. Naturwissenschaften 88:193– the tree. Nature 356:121–125. 200. Novacek, M. J. 1994. Morphological and molecular inroads to phylogeny. In L. Grande and O. Rieppel, eds. Interpreting the Hierarchy of Nature: from Systematic Patterns to Evolutionary Process Theories. Academic Press, New York, p. 85–132. Novacek, M. J. 2001. Mammalian phylogeny: Genes and supertrees. Current Biology 11:R573–575. Patterson, C., D. M. Williams, and C. J. Humphries. 1993. Congruence between molecular and morphologi- cal phylogenies. Annual Review of and Systematics 24:153–188. Rieppel, O. 2000. Turtles as diapsid reptiles. Zoologica Scripta 29:199–212. Rieppel, O., and M. deBraga. 1996. Turtles as diapsid reptiles. Nature 384:453–455. Rieppel, O., and R. R. Reiz. 1999. The origin and early evolution of turtles. Annual Review of Ecology and Systematics 30:1–22. Seilacher, A. 1994. Early multicellular life: Late Proterozoic fossils and the Cambrian explosion. In S. Bengston, ed. Early Life on Earth. Nobel Symposium no. 84. Columbia University Press, New York. p. 389–400. Shu, D.-G., H.-L. Luo, S. Conway Morris, X.-L. Zhang, S.-X. Hu, L. Chen, J. Han, M. Zhu, Y. Li, and L.-Z. Chen. 1999. Lower Cambrian vertebrates from south China. Nature 402:42–46. Valentine, J. W., D. Jablonski, and D. H. Erwin. 1999. Fossils, molecules and embryos: new perspectives on the Cambrian explosion. Development 126:851–859. Wells, J. 2000. Icons of evolution: science or myth?: why much of what we teach about evolution is wrong. Regnery, Washington DC, 338p.

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