BOOK REVIEWS saurs, probably sharing a common ancestor with the dromaeosaurids. But dromaeosaurids are not known before the latter half of the Cactaceous. For Proloauis The Rise of Birds: 225 Million Years of Evolution. to have evolved from dromaeosaurids means the Sankar Chatterjee. 1997. The Johns Hopkins dromaeosaurids would have about 125 million years of University Press, Baltimore, MD. 312 p. $39-95 undiscovered history, dating back to the Triassic, during I definitely recommend Dr. Sankar Chatterjee's book to which they changed very little. Not only would those interested in the origin and evolution of birds, dromaeosaurid evolution be pushed back to the early although I (and others) disagree with some of Chatterjee's Triassic, so would most of the divergences of the major ideas. Much of the book makes detailed comparisons of lineages in the dinosaur clade, with undiscovered fossil the anatomical features of birds and their relatives in the lineages for each. Again, this is technically possible, but archosaurian lineage, making much of it inaccessible is it probable or reasonable? It is a very large assump- without a good anatomy background. The strengths of tion in need of much more data. Cladistic analysis is a the book lie in its anatomical comparisons and its attempt powerful method of determining evolutionary relation- to define Protoauis' position in avian evolution. The ships between organisms, but one weakness is its portions dealing with bird flight and the evolution of inability to consider time as part of the equation. The flight have some interesting hypotheses as well as some question in the Protoauis case is not whether it was weaknesses. possible, but rather is there convincing data that it did The most important part of Chatterjee's book is the happen and that Protoauis is a more modern bird than analysis of his most important fossil find, Protoauis lex- Archaeopteryx? It is an interesting hypothesis, but the ens is. Since its discovery in 1983, Protoauis has generated case is not convincing yet. Much more fossil evidence controversy, debate, and fascination, so a detailed ac- will be needed to make this case. count of Protoauis has been long awaited. Chatterjee's The general consensus that birds evolved from small book brings information from several of his publications theropod dinosaurs is so widely held that many people on Protoauis together in one volume. Unfortunately, one may not realize how difficult that consensus has been to key element missing from Chatterjee's book are photo- reach, or why determining the evolutionary history of graphs of the skeletal elements of Protoauis so that birds has been so difficult. Chatterjee gives a general readers can judge for themselves the accuracy of the treatment of the competing theories of the origin of reconstructions and drawings done by Chatterjee and birds, but does it in the tenth chapter, not near the his staff. For example, Chatterjee's drawings indicate beginning of the book. His summary is too brief and possible quill knobs on the ulna and metacarpals II and does not clearly convey why determining the ancestors III, which would be strong evidence that Protoauis was of birds has been so difficult. There are several very a bird with flight feathers capable of generating aero- bird-like archosaur lineages, often showing evolutionary dynamic forces. But without photographs of the actual convergences. This is important because if Chatterjee is fossils, the readers are not able to make their own correct and Protoauis is in the bird lineage, then the judgments on the issue, or other interpretations of current bird-dromaeosaurid hypothesis will have to be skeletal characters. seriously reevaluated in light of the absence of Triassic Chatterjee claims Protoauis' skeleton shows signs of or even early Jurrasic dromaeosaurid fossils. A final being more advanced than Archaeopteryx. Chatterjee consensus on the identity and evolutionary position of says Protoauis would be capable of powered flight, a Protoauis has not been reached. trait that is uncertain for Archaeopteryx. If Protoavis is Although Chatterjee agrees with the hypothesis of more advanced than Archaeopteryx, then one might ex- birds as dinosaur descendants, he has broken ranks pect Protoauis to appear more recently in the fossil with the dinosaur camp on the origin of bird flight. record than Archaeopteryx, yet Protoauis predates There are two predominant schools of thought on the Archaeopteryx by about 75 million years. This may seem origin of bird flight. One says birds are dinosaur unreasonable at first, but it is possible Archaeopteryx descendants. Dinosaurs were strictly terrestrial so there- was a "living fossil" in its day, much like the coelacanth fore bird flight evolved from the ground up. The other is today. There are difficulties determining if Protoauis school says the aerodynamics and biomechanics clearly is more advanced than Archaeopteryx. For example, show bird flight must have evolved from the trees one character shared by both Protoauis and modern down and since dinosaurs were terrestrial, birds must birds, but not found in Archaeopteryx, is the loss of a have evolved from a non-dinosaurian archosaur. couple of bony struts in the skull, which makes the up- Chatterjee assumes that, of the many small dinosaurs, per jaw movable. Chatterjee cites this as one of the some must have been able to climb trees and one group characters showing Protoauis as more modern than evolved flight from the trees down. If birds are dinosaur Archaeopteryx. It is uncertain if modern birds inherited descendants, then I would agree with Chatterjee: Look this feature from Protoauis, or if it is convergent evolu- for the ancestors of birds among small, tree climbing tion. Cladistic analysis depends on being able to differ- dinosaurs. Chatterjee also presents the hypothesis that entiate between convergence and common ancestry, climbing by the ancestors of birds and early birds might which is difficult to determine when specimens are few. have been responsible for the migration of the biceps Chatterjee agrees with the prevailing hypothesis that tubercle, leading to the supracoracoideus system birds birds are descendants of maniraptoran theropod dino- use to raise their wings. The evolution of the supracora- 96 BOOK REVIEWS VOL. 99

coideus system has been difficult to explain. So, this The other areas of the book are well done, including hypothesis deserves serious investigation. a look at the Cretaceous extinction and Dr. Chatterjee's Chatterjee's model for the arboreal evolution of flight work on the impact theory of the Cretaceous extinction, does not differ greatly from the model of Bock and and overview of other Mesozoic birds, the rise of birds others (jumping between branches leads to parachuting, after the Cretaceous extinction, and concluding ap- then gliding, then powered flight) with one large excep- propriately with the chapter "Birds and Humans." The tion. Chatterjee proposes two steps in the evolution of last chapter recounts the impact humans have had on bird flight where the ancestors of birds initially jump birds as well as stating why birds are important to into water feet first to break their fall, which evolved humans. The final line of Dr. Chatterjee's book says of into diving into the water head first. Although jumping birds and humans, "This is the only home in the entire into water can break an animal's fall, doing so is not solar system we can share together." Let's hope we are risk free, with many potential and often hidden hazards willing enough to share the planet that we can stop the in the water. Diving head first into water is a specialized loss of birds and other species. STEVHN A. EDINGER and dangerous activity, used by a limited number of Department of Biological Sciences animals in certain circumstances. This hypothesis seems Ohio University very unlikely and very difficult to test. Athens, OH 45701-2979

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