Controversy regarding avian origins originated with the 19th-century discovery of the iconic Archaeopteryx. The Urvogel possessed a seemingly dinosaur-like skeleton yet was cloaked in a set of exquisitely preserved, modern-appearing feathers. More recently, discoveries of supposedly “feathered dinosaurs” from Mesozoic lake deposits in China have provided well-publicized support for the notion that birds evolved from the “raptor-like” dromaeosaurid theropod dinosaurs. Indeed, recent conventional wisdom holds that birds are little more than “flying dinosaurs.” Nevertheless, a cadre of respected researchers in this field remain unconvinced. In his latest book, Riddle of the Feathered Dragons: Hidden Birds of China, Alan Feduccia has assembled a comprehensive, lucid, and detailed analysis of the importance of these new specimens and what they may, or may not, tell us about avian origins.
Feduccia, an experienced paleo-ornithologist, has gained a reputation for cautious skepticism regarding the dinosaur—bird nexus. In this book he challenges entrenched orthodoxy, drawing sharp focus on some of the sensationalistic, if questionable, science that has been marshaled to support the theropod—bird link. Feduccia cautions against what he and others see as a “verificationist” approach to the complex and rapidly expanding fossil data, noting that the field of bird origins has too often taken an overtly political tone that smacks of “science by consensus,” embodied by statements such as those by Henry Gee, a senior editor of the journal Nature, that “birds are dinosaurs: the debate is over,” and Richard Prum's assertion that “it is time to abandon debate on the theropod origin of birds” (see p. 7). Rather, Feduccia urges for the application of the traditional approach of proposing and testing viable alternative hypotheses that are indicated by these emerging data, rather than shoe-horning them into support of the existing hypothesis. In Feathered Dragons, Feduccia provides the reader with a variety of compelling, but often ignored, data that are at odds with a derived theropod ancestry for birds. Among the examples of contradictory evidence that he showcases is the case of non-homology of the manual digits in theropods and birds—that although the three digits on the hands of theropods and birds often bear remarkable anatomical similarities, multiple developmental studies have indicated that the avian hand comprises digits 2, 3, and 4 whereas the generalized theropod hand is broadly acknowledged to be made up of digits 1,2, and 3. To account for this discrepancy, bird—dino supporters have invoked a genetic frame-shift mutation that altered the identity of the digits, an unprecedented event in amniotes.
In another example of a report that strains credulity, Feduccia examines the claims of preserved soft tissues from a 75-millionyear-old T. rex fossil. Several papers published in high-profile journals claimed to have recovered tissues including collagen, blood vessels, and even red blood cells from the femur of a tyrannosaurid, and to have extracted DNA that resembled that of birds—extraordinary assertions that made headlines. As Feduccia points out, follow-up analyses that cast serious doubts on these claims received little fanfare.
Feduccia also discusses the bombshell news from 1997, when the first of many “feathered theropods” began to emerge from China. These reports shook the scientific world and made headlines across the globe. These fossils were heralded as the final “nail in the coffin” for doubters of a close theropod—bird linkage. Feduccia provides a comprehensive treatment of the literature on the subject and shows that although many of the fossils are indeed feathered (and are also birds), a number of key specimens of more basal theropods described as “feathered” or “protofeathered” (i.e., possessing supposed simple filamentous integumentary fuzz) are in reality more likely to represent unusual preservation of dermal (within the skin) collagen fibers. These are just a few of the pieces of possibly dubious evidence that have been used to verify a dinosaurian ancestry for birds. Feduccia argues that these suspect studies should, at the very least, provoke a reexamination of the questions at hand.
Additionally, he provides an excellent treatment of the diverse fossils of enantiornithine (archaic “opposite” birds) and basal members of ornithiurine (modern) bird lineages from northeast China. He also evaluates a number of the curious, small dromaeosaurid microraptors, Velociraptor-like animals with arboreal adaptations (which included a perching foot and feathers forming wing surfaces on both fore- and hindlimbs). What to do with this avalanche of data? Feduccia urges that it be reanalyzed without a predetermined conclusion in mind.
That this controversy has become so bitterly fought is a bit of a wonder, in that both sides agree that birds and dinosaurs are closely related—the issue balances on when and where birds diverged from within the archosaurs. Thus, perhaps the most surprising suggestion Feduccia offers, and one that deserves a much longer look from anyone interested in these questions, is that data drawn from the myriad of new fossils could actually be turning conventional wisdom on its head (literally)—that is, the very birdlike dinosaurs such as the iconic ‘raptors of Jurassic Park (e.g., Velociraptor and its relatives), the enigmatic troodontids, and the bizarre beaked oviraptorosaurs—long considered to be among the more derived theropods—are, in fact, members of an extensive adaptive radiation of volant and secondarily flightless birds! Those who have followed Feduccia's work over the years will recognize that this conclusion is a major shift in his views, and that his ability to deal with the new evidence in such an unbiased and creative manner is the mark of a uniquely sharp and innovative scientific mind. Whether one ultimately agrees with Feduccia or not, Feathered Dragons: Hidden Birds of China is a “must read” for anyone interested in these questions and will prod its readers to rethink received wisdom on the subject of the evolution of birds.
