Mistaken Extinction. Dinosaur Evolution and the Origin of Birds, The

Auk, The, Apr 1999 by Bock, Walter J

The Mistaken Extinction. Dinosaur Evolution and the Origin of Birds.-Lowell Dingus and Timothy Rowe. 1997. W. H. Freeman and Company, New York. xiv 332 pp., numerous text illustrations. ISBN 07167-2994-X. $34.95.-The Mistaken Extinction is another of the books published over the past several years dealing with the evolutionary origin and radiation of birds. This volume is presented from a cladistic point of view and is based on the conclusion that birds evolved from an advanced group of dinosaurs-the Maniraptora of the Theropoda. The Theropoda is a subgroup of the Saurischia (reptilehipped dinosaurs), which in turn is a subgroup of the Dinosauria, which is a subgroup of the Archosauria, and which is finally a subgroup of the Archosauriformes-the archosaurian or ruling reptiles. This volume is written for the general biologist and the lay public with a relaxed, easy-to-read style and from a personal viewpoint. The book is well illustrated, although it would have been better to have the illustrations numbered.

Probably because this book was issued in two forms-one for the lay public and one for academic biologists-it has two ISBN numbers; I have no idea whether the copy before me is the academic one or the lay-public one. Moreover, the copyright is 1998, but the first printing of this book is 1997, although the Library of Congress cataloging information gives the publication date as 1998. Hence, I am not certain just how to cite this book (the citation at the start is that available from the publisher's web site).

The thrust of this volume is that because birds are dinosaurs, dinosaurs did not become extinct at the end of the Mesozoic-hence the title The Mistaken Extinction. Yet, it is interesting that the first 100 pages discuss theories about the extinction of the dinosaurs, especially marshaling the evidence for the large meteorite impact identified as the Chicxulub Crater at the edge of the Yucatan Peninsula as the "smoking gun" responsible for the extinction event at the K-T boundary. Several interesting aspects of this extinction event are left undiscussed in this volume.

First and most interesting of these is the ease with which paleontologists talk about the causes of extinction of organisms, including large taxa and major parts of the biosphere. Yet, ascertaining the causes for extinction of organisms is a most difficult task for neontologists. It should be noted that even if excellent evidence exists for a large meteorite impact that formed the Chicxulub Crater, all that can be said is that the time of occurrence of this meteorite impact and of the final extinction of the nonflying dinosaurs (and possibly a lot of other species of animals) are correlated. Causal relationships still remain to be determined.

The second problem is that if birds did descend from theropod dinosaurs, and if this relationship is used by many dinosaur paleontologists, including Dingus and Rowe, to argue that physiological properties (e.g. homoiothermy) of dinosaurs are similar to those of birds, then it is far more difficult to claim that the nonflying dinosaurs-but not birds-became extinct as a result of the effects of this meteorite impact. This is especially difficult to understand because Dingus and Rowe (Chapter 15) argue against the hypothesis of Alan Feduccia that many groups of birds died out at the end of the Mesozoic and that the modern avian groups present in the Tertiary radiated from a few lineages that survived the extinction event at the end of the Cretaceous.

Dingus and Rowe accept the hypothesis that birds evolved from an advanced group of theropod dinosaurs and are most closely related to the Dromaeosauridae, which includes such genera as Deinonychus and Velociraptor. They illustrate this relationship with numerous cladograms, none of which indicates possible times for the splits between sister taxa. The problem is that many of these splits, including almost all between sister taxa of the entire dinosaur radiation, would have to be pushed back into the middle of the Jurassic (prior to the date of Archaeopteryx), or possibly early in the Triassic, if Protoavis is an ancestral bird. Yet, few fossil remains provide evidence for these early dichotomies, and Dingus and Rowe had to advance the concept of ghost trails to account for all of the missing lineages. One gets the impression that hypothesis is piled on hypothesis to support the favored idea so that the entire argument starts to become rather unparsimonious.

Several serious matters undermine the hypothesis advocated by Dingus and Rowe on the theropod origin of birds. The first is that they dismiss, almost out of hand, all discussion of the Triassic Protoavis described by Sanker Chatterjee (see my review of his book, Auk 115:808-809, 1998). It is not true that only Chatterjee and Larry Martin accept that Protoavis is an ancestral bird. Evgeny Kurochkin, who has examined more Mesozoic avian fossils than any other avian paleontologist, has accepted Protoavis as an early ancestral bird and has placed it in the subclass Praeornithurae, which is at the base of the radiation of the Ornithurae (Archaeopteryx 13:47-66, 1995). Kurochkin places Archaeopteryx and the Enanthiornithes in the subclass Sauriurae, which is a side branch to the radiation leading to the living birds. If the Triassic Protoavis is an ancestral bird for which there is some good evidence, then the origins of birds would be pushed back to the mid-Triassic or earlier, and all of the ghost lineages of dinosaurs associated with the hypothesis that birds descended from the Maniraptora would have to be pushed back to the early Triassic, a time before the earliest known dinosaur fossils.