Feathered Dragons: Studies on the Transition from Dinosaurs to Birds

Auk, The, Apr 2005 by James, Frances C, Pourtless, John A IV

Feathered Dragons: Studies on the Transition from Dinosaurs to Birds. -Philip J. Currie, Eva B. Koppelhus, Martin A. Shugar, and Joanna L. Wright, Eds. 2004. Indiana University Press, Bloomington. xiii 361 pp. ISBN 0-253-34373-9. Cloth, $49.95.-The discovery in 1993, in Upper Cretaceous sediments in Montana, of a remarkably complete skeleton of a subadult birdlike dinosaur, Bambiraptor feinbergi (Burnham et al. 1997, 2000), prompted Martin Shugar to organize the Florida Symposium on Dinosaur-Bird Evolution, an international event held on 7 and 8 April 2000 in Fort Lauderdale. The guest of honor was John Ostrom, the Yale paleontologist whose work initiated the current resurgence-now in its fourth decade -of interest in the origin of birds. Bambiraptor feinbergi was on display at the meeting, along with some new fossils from China. Most of the papers in this volume were presented orally at that meeting.

The book has a section of fanciful color plates of drawings of dinosaurs that suit the book's flamboyant title, but the text has a serious scientific intent. Even so, nearly every chapter repeats the mantra of the birds-are-dinosaurs movement, and the foreword assures the reader that, because the "level of controversy over bird origins has waned" (p. xii), attention can now turn to other issues, such as the evolution of feathers and flight. In general, the book reflects the heady enthusiasm of the many paleontologists and systematists in the 1990s who were interpreting the wonderful new fossil discoveries in Early Cretaceous deposits in China and elsewhere as increasing support for the view that birds evolved from certain maniraptoran theropod dinosaurs (troodontids and dromaeosaurs).

After an introductory tribute by Robert Bakker to Edward Hitchcock's mid-19th-century studies of dinosaur footprints found in the Connecticut Valley redbeds, the 14 chapters that report original work are organized into three sections: two on the setting; six on osteology and ichnology (tracks); and six on eggs, nests, feathers, and flight. Dale Russell compares dinosaur assemblages of central Asia and North America, emphasizing the importance of the many specimens of well-preserved small birdlike dinosaurs found in the dune fields of Mongolia, a region that was isolated in the Late Cretaceous period. Most relevant for the subject of this book are the oviraptorosaurs (Oviraptor), troodontids (Saurornithoides), and dromaeosaurs (Velociraptor), plus two primitive "theropod-mimic" birds (Mononykus and Shuvuuia). Russell reminds readers that we do not know the biogeographic origin of birds, or theropods, or dinosaurs. In Chapter 2, Gregory Retallack argues that large-scale acidification was the most direct cause of the selective extinctions of animals and plants that occurred 65 million years ago, after the now-famous meteorite impact that marked the transition from the Cretaceous to the Tertiary period, taking with it all the dinosaurs, the enantiornithine birds, and many other taxa.

The section on osteology and ichnology begins with David Burnham's formal description of the virtually complete skull and postcranium of the holotype of Bambiraptor feinbergi, based on the individual bones; the description is supplemented with photographs of the skull and drawings of most of the bones. Additional study has suggested that this dromaeosaurid is less velociraptorine than stated here (Senter et al. 2004). The forelimb is very similar to that of Archaeopteryx, but there is no discussion of whether Bambiraptor may indeed have been a bird.

The next three papers describe new details of specimens from Canada and Mongolia. Then Fernando Novas, without suggesting that Unenlagia might be a bird, argues that its ilium is even more birdlike than that of dromaeosaurids, and Joanna Wright reviews information about the birdlike features of dinosaur footprints. Overall, this section adds new information about the birdlike osteology of various maniraptorans.

section 3 begins with an important paper by Gerald Grellet-Tinner and Luis Chiappe that compares the microstructures of eggs and the nesting behaviors of turtles, crocodilians, dinosaurs, and birds. Like birds, troodontids and oviraptorids laid eggs at daily intervals in open nests (not covered by substrate). Like birds, they had asymmetrical eggs with at least two eggshell layers separated by an aprismatic delimitation. David Varricchio and Frankie Jackson add details to information about Troodon and argue that, because delayed incubation and brooding behavior must have synchronized the hatching of eggs, the body temperature of the adult must have at least temporarily surpassed that of the environment. The argument by Thomas Hopp and Mark Orsen in Chapter 11 that brooding behavior selected for the evolution of long flight feathers is supported only by some drawings of birds in unnatural poses. Contrary to Ostrom, Sankar Chatterjee and R. J. Templin consider the cursorial model for the origin of flight to be biomechanically untenable. They construct a thesis that involves the theropod origin of birds arid the arboreal origin of flight and support it by putting the new Chinese fossils in an order that fits that scenario.