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Home , Alan Feduccia, Gerhard Heilmann, Sinornis, The Origin of Birds

Palaeontologia Electronica http://palaeo-electronica.org

Dinosaurs of the Air: The Evolution and Loss of Flight in and Birds1

Mesozoic : Above the Heads of Dinosaurs2

reviewed by Kevin Middleton

1by Gregory S. Paul Johns Hopkins University Press, Baltimore, 2002, 472 pp. ISBN: 0-8018-6763-0 $54.00 (cloth)

2edited by Luis M. Chiappe and Lawrence M. Witmer University of California Press, Berkeley and Los Angeles, 2002, 536 pp. ISBN: 0-520-20094-2. $95.00 (cloth)

When Ostrom (1973, and early evolution of 1974, 1975, 1976) and birds. Coupled with this Bakker and Galton (1974) interest in avian relation- revived interest in an evo- ships is the frequently lutionary relationship contentious issue of the between theropod dino- . Two saurs and birds, Archae- new books take radically opteryx, , and different approaches in were the their treatments of these only well-known species topics. of birds. Dur- In Dinosaurs of the ing the past fifteen years Air: The Evolution and fossil evidence of the diversity of Mesozoic birds Loss of Flight in Dinosaurs and Birds (The Johns and their non-avian theropod relatives has grown Hopkins University Press, 2002) Gregory Paul lik- tremendously. Whereas only a few fossil avian taxa ens himself to a modern day . In were available to Gauthier (1986) in his landmark 1926, Heilmann, an illustrator like Paul, wrote The cladistic analysis of the systematic position of . After presenting a great deal of birds, a tremendous number of avian species are comparative anatomical data suggesting a link now known from the Mesozoic, and new taxa are between birds and theropod dinosaurs, Heilmann being described at a remarkable pace. infamously concluded that the two could not be Recent years have seen a proliferation of closely related. At the time, had not been books on the increasingly broad topic of the origin discovered among non-avian theropods, and,

Middleton, Kevin. 2003.Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds; and Mesozoic Birds: Above the Heads of Dinosaurs. Palaeontologia Electronica, 6: 5, book review 1, 148KB; http://palaeo-electronica.org/paleo/toc.htm MIDDLETON: DINOSAURS OF THE AIR AND MESOZOIC BIRDS

under a strict interpretation of Dollo's Law, Heil- support his claim, most of which is presented in an mann hypothesized that birds evolved from a unjustifiably authoritative style, Bakker oversimpli- group of basal , the "thecodonts" fies the history and present state of stud- (Gauthier, 1986). Whereas Heilmann failed ies." Data and conjecture are rarely delineated in because of an incomplete fossil record - theropod Dinosaurs of the Air. clavicles were not discovered until 1936 - Paul's For example, Paul states that "flight, even the effort to present a synthetic book on the origin of flapping version, is a comparatively simple opera- birds and of avian flight fails for rather different rea- tion" (p. 131). He then erroneously compares flap- sons. ping flight in birds to the flight of fixed-wing aircraft. Paul's book follows in the footsteps of recent He presents his analysis of avian flight as if it is quasi-technical books on birds and their dinosau- well supported by scientific evidence, although, rian ancestors. This lineage of nominally scientific even after more than 50 years of research, the books began in 1986 with the publication of Dino- mechanisms of avian flight - anatomical, biome- saur Heresies: New Theories Unlocking the Mys- chanical, aerodynamic - are still not well under- tery of the Dinosaurs and Their Extinction by stood. Furthermore, Paul virtually ignores fifteen Robert T. Bakker, which quickly became the bible years of research on the kinematics, neuromuscu- of self-proclaimed "dinosaurologists," of whom lar control, and aerodynamics of avian flight. It is Paul is one. Bakker's book was followed shortly by egregious to present such a scenario as though it Paul's first book, Predatory Dinosaurs of the World: is based upon actual data rather than just his own A Complete Illustrated Guide (1988), which carried intuition. When reviewing Feduccia's The Origin Bakker's analyses several steps further. After the and , Brush (1997, p. 450) cau- tremendous recent growth in the number of Meso- tioned, "The reader must temper the words know- zoic fossils, several authors have written ing that the use of assumptions about evolutionary books in which they attempt to integrate the new processes or adaptational scenarios can be mis- fossil avian and non-avian theropod discoveries of leading when trying to understand historical events the last fifteen years to develop a coherent picture or relationships." Readers of Dinosaurs of the Air of the origin and evolution of birds and avian flight. would do well to follow this advice. These books include 's The Origin Frequently Paul summarily dismisses con- and Evolution of Birds (1996), The Rise of Birds: trasting viewpoints. For example, he writes that "... 225 Million Years of Evolution by Sankar Chatter- Ruben and co-workers' analysis is without suffi- jee (1997), and Taking Wing: and cient basis and must be rejected" (p. 202). Padian the Evolution of , written by Pat Shipman (1989, p. 283) noted a similar pattern in Paul's first (1998). book, Predatory Dinosaurs of the World, and com- These books have been applauded for their mented that "Paul takes a confident, assertive attempts to bring and evolution to the tone, but often fails to credit or discuss the ideas of general public in an accessible manner. However, others with more than a curt dismissal, notably they also have been soundly criticized in the pale- when they controvert his own." ontological community for their speculative and Early in Dinosaurs of the Air, Paul states that unfounded assertions as well as their frequent "a computer generated cladistic analysis of bird ori- summary dismissal or outright omission of sources gins is premature at this time" (p. 21). His attitude or contrasting views. Both of these faults contribute reveals a misunderstanding of the goal of cladistic to an overall lack of scientific rigor. While the aims analysis: to generate hypotheses of relationships of each book have been quite different, their collec- between organisms. To say that not enough com- tive failures are startlingly similar. plete specimens are known to even try a cladistic Unfortunately, Paul's new book offers more of analysis is to defeat the purpose and render any the same and can be regarded as just another evolutionary hypotheses useless. I agree with entry in this increasingly crowded bookshelf. Criti- Clark et al. (in Mesozoic Birds; p. 33), who state cisms that have previously been leveled against that "the importance of phylogenetic hypotheses to the books by Bakker, Paul, Feduccia, Chatterjee, the study of evolution cannot be overstated." Any and Shipman are equally applicable to Dinosaurs discussion of evolution must be predicated upon of the Air. an hypothesis of relationships. Presently the tool One of the principal criticisms of these books requiring the fewest number of untestable hypothe- has been that they rely on confident assertion ses is cladistic analysis. Because a cladogram, by rather than scientific data to support their hypothe- definition, has the fewest ad hoc hypotheses of ses. Of Bakker's Dinosaur Heresies, Ostrom change, any other methodology will have less (1987, p. 58) wrote, "In marshaling evidence to explanatory power.

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In a sense, Paul's line of argument throughout gin of birds and evolution of flight, rather than the the book is backward. He begins the book with an uneven, sparsely documented presentations that overview of non-avian and avian theropod skeletal have been offered so far. The authors expect to be anatomy. From this base, he discusses forelimb taken seriously by the paleontological community, function and "The Beginnings of Flight," moves on but the approach used precludes such acceptance. to "The Early Evolution of Flight," and concludes In conclusion, I agree with Benton's (1990, p. with "Who is Related to Whom and Why?" By put- 350) assessment that Predatory Dinosaurs of the ting function and evolution before phylogeny, in the World "will do great good in promoting paleobiol- end he is left searching for the most likely organism ogy to a wide readership, but it may do great harm in which flight would have evolved, as he imagines to the professional study of dinosaurs." While the it to have evolved. He goes so far as to say, "The goals may be admirable, the methods employed by methodology I use here presumes that the pres- Paul in both Predatory Dinosaurs of the World and ence of a birdlike character in a group that is Dinosaurs of the Air misrepresent the science of clearly unrelated to birds is not of phylogenetic paleontology and the study of evolution and ulti- importance" (p. 171). mately discredit the science as a whole. The end result and perhaps most damning In contrast, Mesozoic Birds: Above the Heads fault is that Dinosaurs of the Air and the other of Dinosaurs (University of California Press, 2002), books mentioned herein simply lack scientific rigor. edited by Luis M. Chiappe and Lawrence M. Wit- They are not reviewed by peers and thus are not mer, is a multi-author work with two purposes: first, subject to the same scrutiny. I will not contend that to survey the present state of Mesozoic avian pale- peer review is a cure-all for poor science or faulty ontology; and, second, to provide full descriptions reasoning, but some of the more fatuous state- of specimens previously only preliminarily dis- ments made by these authors certainly would not cussed in the literature. pass unnoticed. The failure of these books was The first two chapters, under the heading "The recognized by Crompton and Gatesy (1989, p. Archosaurian Heritage of Birds," are outstanding 113), who observed, in reference to Predatory and should be required reading for those interested Dinosaurs of the World, "This is not to say that in avian evolution. In Chapter 1, Witmer provides a there is no place for such individual views, but they refreshingly evenhanded review of the debate on need to be balanced in some way so that readers bird origins, both past problems and emergent who are not familiar with the field will recognize questions. With the admonition that "bombast is a that not all paleontologists would agree." They poor substitute for evidence" (p. 4), Witmer exam- added that "Paul fails to give the curious reader a ines the published data on the questions of (1) the view of how the science of paleontology works; importance of the evolutionary relationship of birds instead, anything goes" (p. 113). among Reptilia (to allow inferences both about One could reasonably ask: Why are these their ancestors and descendants); (2) the validity of books published? And do they have any scientific Archaeopteryx as a central in the debate value whatsoever? The first question is more easily about avian origins (warranted); and, (3) the impor- answered; simply, dinosaurs sell books (or scien- tance of in the debate (minimal). tific magazines, but that topic is better left to The most significant portion of Witmer's chap- another editorial). The second, evaluating the sci- ter examines the relationship between the origin of entific merit of these books, is more troublesome. birds and the evolution of avian flight. These two The hypotheses proposed by Gregory Paul and issues have, in too many analyses, become synon- authors of books I have mentioned here could very ymous. Witmer argues that, while well have appeared in the scientific literature had is a genealogical question, the origin of flight is an the authors been interested in pursuing that route. evolutionary question; the latter relies on the Indeed, parts of all of the books mentions here, hypotheses of the former. Soberly, Witmer says except for Shipman's Taking Wing, had appeared that "it is conceivable that the origin of flight – as a in scientific journals. In this way, the books are part matter of scientific discourse – is out of reach." review and part speculation, aimed at a nonprofes- While experimental data (e.g., Dial, 2003) may pro- sional audience. It is with the speculative portion vide novel hypotheses for the origin of flight, recon- that I take issue, for significant portions of the structing a complex behavior that evolved at least books are simply opinion disguised as science. 145 million years ago may ultimately prove impos- Paul et al. some day may be shown to be cor- sible. rect, but their present methods are a distortion of In the second chapter, Clark et al. present a evidence-based, hypothesis-driven science. I phylogenetic analysis of theropod relationships. would welcome a well-reasoned analysis of the ori- Although the lengthy process of book publishing

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means that new taxa often are omitted, the authors In addition to Lockley's and Rainforth's chap- did include recently described taxa such as ter reviewing avian tracks from the Mesozoic, Kell- as well as several taxa whose phyloge- ner reviews avian diversity. Although netic relationships have been uncertain (e.g., Cau- admirably detailing the range of known dipteryx and alvarezsaurids). However, the most from the Mesozoic, Kellner's chapter on feathers is important aspect of this chapter may be that the particularly lacking. He omits all of the known non- authors additionally present a clear and concise avian theropod taxa that are known to have feath- explanation of the central principles of cladistic ers or feather-like integumentary structures - e.g., analysis. , , , Part II contains three chapters covering histor- , and - instead ically controversial taxa. With the goal of fostering focusing on isolated feathers. renewed research, Vickers-Rich et al. present a The final section of the book concerns "Func- pictorial atlas of portentosus, an enig- tional Morphology and Evolution." In "Bone Micro- matic theropod that has been hypothesized to be a structure of Early Birds" Chinsamy reviews past flightless bird. Two chapters address members of work on bone microstructure and discusses the clade . Chiappe et al. discuss present areas of research. Whereas early paleo- the skeletal material of alvarezsaurids, which now histology was mainly concerned with potential phy- are known from Asia, North America, and South logenetic information to be garnered, recent work America. The authors note that the phylogenetic has been used to shed light on paleophysiology relationships of alvarezsaurids among other thero- and growth rates of Mesozoic birds. New data are pods are complicated by their highly apomorphic presented on the bone histology of Cimolopteryx, skeletons. , and an unnamed taxon. Novas and Pol (Chapter 5) present a phyloge- In "Locomotor Evolution on the Line to Mod- netic analysis which places alvarezsaurids well ern Birds", Gatesy draws on studies of anatomy in outside as a distinct clade of coelurosaurs. fossil and extant archosaurs as well as kinematic Their results agree broadly with those of Clark et and muscle activity pattern data for extant archo- al. (Chapter 2), but disagree with Chiappe (Chapter saurs (alligators and birds) to trace the evolution of 20, see below), who found that Alvarezsauridae theropod locomotion. Gatesy uses optimization to was the sister group of Archaeopteryx. The dispar- assign character states to internal nodes of the cla- ity in these conclusions may result from differences dogram and, by only choosing certain nodes at in taxa that were included in the different analyses. which to reconstruct ancestors, is able to assign Novas and Pol as well as Clark et al. focused their states to nodes that may be ambiguous lower on analyses more broadly on non-avian theropods, the cladogram. The book concludes with a cladistic while Chiappe mainly was concerned with the analysis of Mesozoic birds by Chiappe. Unfortu- interrelationships among birds and their close rela- nately, the pace of new discoveries makes this tives. The results found by Novas and Pol and by chapter somewhat dated, as many new taxa are Clark et al. may not have even been possible in omitted from the analysis. These include both Chiappe's analysis. basal (e.g., and ) and derived The third section of the book is comprised of forms (e.g., and ) (Zhou and systematic overviews of various clades (Archaeop- Zhang, 2002a, 2002b, 2001). teryx, Chinese birds, Euenantiornithes, Mesozoic Mesozoic Birds is a significant and important Neornithes), longer anatomical descriptions book that will be particularly useful to paleontolo- (, Sinornis, Noguerornis, , Pata- gists and ornithologists alike. Despite the pub- gopteryx, ), and review chapters on lisher's claims, it is not for the nonspecialist, as Mesozoic feathers and avian tracks. Because phy- technical terms and anatomical minutiae are not logenetic and subsequent functional hypotheses likely to be easily digested by the lay reader. will be refined as new specimens are described, Delays associated with publication raise two the full descriptions are perhaps the most lasting issues. First, the anatomical descriptions may have contribution of this volume. Many of these descrip- benefited from more rapid publication in scientific tions, particularly those of Sinornis and Vorona, journals. Second, phylogenetic analyses may not have been much anticipated by researchers. Fur- belong in a book like Mesozoic Birds because the thermore, those of Eoalulavis and analyses are likely to be outdated as soon as they are important for the critical positions that these are published. However, these problems are rela- taxa occupy in phylogenetic analyses. tively minor and do not detract significantly from what is, overall, an excellent volume.

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REFERENCES Heilmann, G. 1926. The Origin of Birds. Witherby, Lon- don. Bakker, R.T. and Galton, P.M. 1974. Dinosaurian mono- Ostrom, J.H. 1973. The ancestry of birds. Nature, phyly and a new class of vertebrates. Nature, 242:136. 248:168-172. Ostrom, J.H. 1974. Archaeopteryx and the origin of flight. Bakker, R.T. 1986. Dinosaur Heresies: New Theories Quarterly Review of , 49:27-47. Unlocking the Mysteries of the Dinosaurs and Their Ostrom, J.H. 1975. The origin of birds. Annual Review of Extinction. Morrow, New York. Earth and Planetary Sciences, 3:55-77. Benton, M.J. 1990. Predatory Dinosaurs of the World Ostrom, J.H. 1976. Archaeopteryx and the origin of [book review]. Quarterly Review of Biology, 65:349- birds. Biological Journal of the Linnean Society, 8:91- 350. 182. Brush, A.H. The Origin and Evolution of Birds [book Ostrom, J.H. 1987. Dinosaur Heresies [book review]. review]. American Journal of Science, 297:450-452. The Sciences, 27:56-68. Chatterjee, S. 1997. The Rise of Birds: 225 Million Years Padian, K. 1989. Predatory Dinosaurs of the World [book of Evolution. Johns Hopkins University Press, Balti- review]. American Scientist, 77:282-283. more. Paul, G.S. 1988. Predatory Dinosaurs of the World: A Chiappe, L.M. and Witmer, L.M. 2002. Mesozoic Birds: Complete Illustrated Guide, Simon and Schuster, Above the Heads of Dinosaurs. University of Califor- New York. nia Press, Berkeley. Paul, G.S. 2002. Dinosaurs of the Air: The Evolution and Crompton, A.W. and Gatesy, S.M. 1989. Predatory Dino- Loss of Flight in Dinosaurs and Birds. Johns Hopkins saurs of the World [book review]. Scientific American, University Press, Baltimore. 260:110-113. Shipman, P. 1998. Taking Wing: Archaeopteryx and the Dial, K.P. 2003. Wing-assisted incline running and the Evolution of Bird Flight. Simon and Schuster, New evolution of flight. Science, 299: 402-404. York. Feduccia, A. 1996. The Origin and Evolution of Birds. Zhou Z. and Zhang F. 2001. Two new ornithurine birds Yale University Press, New Haven. from the of western Liaoning, Gauthier, J.A. 1986. Saurischian monophyly and the ori- China. Chinese Science Bulletin, 46:1258-1264. gin of birds, p. 1-55. In Padian, K. (ed.), The Origin of Zhou Z. and Zhang F. 2002a. Largest bird from the Early Birds and the Evolution of Flight, number 8 in Mem- Cretaceous and its implications for the earliest avian oirs of the California Academy of Sciences. California ecological diversification. Naturwissenschaften, Academy of Sciences, San Francisco. 89:34-38.

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