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The Origin and Evolution of Birds.

The evolutionary origins of birds and the structural and functional transformations that culminated in the advent of powered flight have been subject to intense debate for more than a century. Over the last decade, however, there has been a veritable avalanche of new fossils and data that bears directly on these issues, including the following: (1) discovery of dinosaurs on nests brooding clutches of eggs (Norell et al. 1995; Varricchio et al. 1997); (2) discovery of exquisitely preserved skeletons of small predatory dinosaurs believed by most paleontologists to be most closely related to birds (Russell and Dong 1993); (3) discovery of a featherlike body covering on an Early Cretaceous predatory dinosaur from China (Gibbons 1996); (4) remarkable discoveries of primitive birds from Cretaceous lake deposits in China, Spain, and Madagascar (Sereno and Rao 1992; Sanz et al. 1995; Hou et al. 1996); (5) phylogenetic analyses based on morphology and molecules that introduce and organize a wealth of new data (Gauthier 1986; Chiappe 1995; Sibley and Ahlquist, 1990); and (6) cineradiographic observation of flight performance in living birds (Jenkins et al. 1988; Gatsey and Dial 1996).

Feduccia's book serves the reader a good sampling of these exciting developments. Handsomely assembled and well-illustrated, this volume covers a broad range of current topics on the early evolution of birds in a way that will be of interest to both the professional and the amateur.

Feduccia begins with an introductory chapter (Feathered Reptiles) reviewing basic avian anatomy and describing specimens of the most famous basal bird, Archaeopteryx. He then outlines the history of nineteenth and early 20th-century ideas concerning the origin of birds in a chapter (Descent of Birds) that begins with an introduction to basal archosaurs and is followed by a somewhat puzzling brief on cladistic methodology, an indictment of the method, and a critique of the currently fashionable "theropod-bird" hypothesis. The next chapter (The Cretaceous-Divers and Seabirds) covers not only the extinct diver Hesperornis and seabird Ichthyornis and closest of kin from the Cretaceous, but also includes a curious pastiche of topics from enantiornithine land birds to DNA-DNA hybridization. The next chapter (Evolution of Flightlessness), as desultory as the last, describes a spectrum of flightless and poorly flying birds. It also covers (in no intelligible order) the fossil record for various subgroups such as doves and parrots and presents detailed arguments regarding the anatomical structure and phylogeny of ratites. The chapter on raptors (Birds of Prey) is mercifully short and better organized. The final, long chapter on "arboreal land birds" (Rise of Land Birds) covers the leftovers, including perching birds, and finishes with an unexpected insert on avian "zoogeographic realms" and an entirely anticlimatic ending entitled "A Final Thought."

The organization of this book leaves something to be desired. It is an unconstrained expansion of Feduccia's former book, The Age of Birds (1980), sections of which are included in every chapter. The majority of the text, nevertheless, is new and covers a remarkable range of topics, some better than others.

Feduccia's update on bird origins and evolution ranks as the most complete introduction to the subject currently available. He has provided encyclopedic coverage of the major finds, their general significance, and their relevance to a wide range of topics, including most prominently the evolution of flight and its reduction or loss. The book's excellent bibliography and index will function as a handy reference and entry into the primary literature. And finally, the number of photographs and illustrations is truly extraordinary. Many of these come from the primary literature and enhance immeasurably the content and utility of the book. Although the quality of the paper is not the best for photographs, this choice of paper may be the reason that the book is priced reasonably despite inclusion of scores of excellent photographs and a wide variety of figures.

On the negative side, the author has a poor grasp of some basic phylogenetic concepts and a less-than-sympathetic attitude toward cladistic methodology - despite admitting that "cladistics does represent the most rigorous method for the analysis of morphology." Rigorous phylogenetic analysis, nonetheless, is precisely the tool that must be applied to the problem at hand: the origin and evolution of birds. This book does not convincingly synthesize Mesozoic avian phylogeny or present a tentative phylogenetic scheme for extant orders. Instead we are presented with a "generalized cladogram" for the Mesozoic and early Cenozoic - i.e., a branching phylogenetic tree without specific character support (Feduccia 1995) - and sorting of modern orders to several groups on the basis of their general body form and lifestyle.

By following this scheme and its attendant hypotheses, Feduccia favors what appears to me to be unlikely or patently unwarranted claims: (1) aves can plausibly be positioned at the base of Archosauria rather than as a subgroup of maniraptoran theropods; (2) Archaeopteryx and Enantiornithes form a monophyletic group (Sauriurae) despite dozens of synapomorphies throughout the skeleton linking the latter with more advanced birds; (3) hesperornithiforms belong in a monophyletic subgroup with Ichthyornis rather than as a more primitive stem group; (4) basic feather structure initially evolved solely in response to aerodynamic constraints rather than functioning as a thermoregulatory covering; and (5) the lineages leading to all modern orders of birds diverged within the Tertiary after a K-T event rather than significantly earlier in the Cretaceous.

Feduccia's critique of cladistic methods borders on the ridiculous. He posits that characters are useless if they cannot be polarized, that cladistics assumes that homoplasy is "relatively rare," that all characters must be given equal weight, that similar structures with different functions cannot be homologous, and that "if one key synapomorphy is falsified, then the remainder of the 'synapomorphies' must be considered to be convergent." Feduccia presents case studies to demonstrate the failure of cladistics in the face of "massive convergence," such as in the repeated evolution of aquatic adaptations among disparate groups living in an aqueous environment. Yet this argument is self-defeating, because a recurring suite of correlated characters suggests character interdependence. Correlated characters should not be evaluated (scored) individually as if they were independent.

In the same pages, Feduccia informs the reader that "Everyone agrees that Archaeopteryx is an archosaur." Why? Feduccia remarks that, besides sharing the antorbital fenestra, basal archosaurs are characterized by "a lower temporal bar, a relatively short neck, and a single row of conical teeth" in the upper and lower jaws. Remarkably enough, this is the only evidence Feduccia offers for granting archosaurian status to Archaeopteryx. And, to confuse matters further, on a subsequent page he draws a close relationship between Archaeopteryx and Megalancosaurus, a specialized lizard-sized reptile from the Triassic that lies outside Archosauria (Renesto 1994). Despite a title promising clues to the origin of birds, Feduccia does not present his own branching hypothesis showing where Archaeopteryx fits into archosaur phylogeny. Until detractors of the dinosaurian hypothesis of bird origins either more convincingly explain away substantial and increasing character support linking nonavian theropods and birds or find substantial support linking birds with a nondinosaurian taxon, the dinosaurian hypothesis for the origin of birds will remain for good reason the most viable explanation of the data.

In conclusion, I recommend the book despite significant shortcomings in organization and phylogenetic rigor. Until a volume appears that incorporates the remarkable new avian fossils currently under study and the new data on avian flight performance, this book will stand as the most complete survey currently available on the early evolution of birds.

LITERATURE CITED

CHIAPPE, L. M. 1995. The first 85 million years of avian evolution. Nature 378:349-355.

GATESY, S. M., AND K. P. DIAL. 1996. Locomotor modules and the evolution of avian flight. Evolution 50:331-40.

GAUTHIER, J. A. 1986. Saurischian monophyly and the origin of birds. Pp. 1-55 in K. Padian, ed. The origin of birds and the evolution of flight. Mem. Calif. Acad. Sci. 8.

GIBBONS, A. 1996. New feathered fossil brings dinosaurs and birds closer. Science 274:720-721.

FEDUCCIA, A. 1980. The age of birds. Harvard Univ. Press, Cambridge, MA.

HOU L., L. D. MARTIN, Z. ZHOU, AND A. FEDUCCIA. 1996. Earliest adaptive radiation of birds revealed by newly discovered Chinese fossils. Science 274:1164-1167.

JENKINS, JR., F. A., K. P. DIAL, AND G. E. GOSLOW JR. 1988. A cineradiographic analysis of bird flight: the wishbone in starlings is a spring. Science 241:1495-1498.

NORELL, M. A., J. M. CLARK, L. M. CHIAPPE, AND D. DASHZEVEG. 1995. A nesting dinosaur. Nature 378:774-776.

RENESTO, S. 1994. Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of northern Italy. J. Vertebr. Paleontol. 14:38-52.

RUSSELL, D. A., AND Z. DONG. 1993. A nearly complete skeleton of a new troodontid dinosaur from the Early Cretaceous of the Ordos Basin, Inner Mongolia, People's Republic of China. Can. J. Earth Sci. 30:2163-2173.

SANZ, J. L., L. M. CHIAPPE, AND A. D. BUSCALIONI. 1995. The osteology of CONCORNIS LACUSTRIS (Aves: Enantiiornithes) from the Lower Cretaceous of Spain and a reexamination of its phylogenetic relationships. Am. Mus. Novit. 3133:1-23.

SERENO, P. C., AND C. RAO. 1992. Early evolution of avian flight and perching: New evidence form the Lower Cretaceous of China. Science 255:845-848.

SIBLEY, C. G., AND J. E. AHLQUIST. 1990. The phylogeny and classification of birds. Yale Univ. Press, New Haven, CT.

VARRICCHIO, D. J., F. JACKSON, J. J. BORKOWSKI, AND J. R. HORNER. 1997. Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits Nature 385:247250.
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Author:Sereno, Paul C.
Publication:Evolution
Article Type:Book Review
Date:Oct 1, 1997
Words:1573
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