Birds are dinosaurs: Simple answer to a complex problem

Auk, The, Oct 2002 by Feduccia, Alan

It has become clear that this problem is far more complex that those on either side of the debate had anticipated, and the real challenge now may be to separate out radiations of secondarily flightless birds from true theropods. And, if birds are, as Paul (2002) argues, derived from theropods and then gave rise to secondarily flightless theropods, the problem of convergence is simply transferred to dromaeosaurs and carnosaurs. Such a convergent pattern may be even more formidable than that proposed between flightless birds and theropods. Either way, if birds were initially derived from dromaeosaurs, then the required character transformations involved going from highly derived sickle second claw to primitive avian claw, highly derived stiffened tail to primitive Archaeopteryx-like tail, and highly derived theropod teeth to primitive bird teeth (Table 1).

Temporal Paradox. -Despite Prum's attempt to dismiss the "temporal paradox" as irrelevant to the debate, it is a problem of great concern to most workers in the field and especially the interested public. In 1999, at a special Florida conference on the dinosaurbird problem, the small, juvenile velociraptorine Bambiraptor was introduced as the then most birdlike theropod ever discovered. Yet, it dates to 70 Ma, that is, some 80 my after the appearance of the earliest known bird Archaeopteryx. As Dodson (2000:504) points out, "The current cladistic analysis of bird origins posits a series of outgroups that postdate the earliest bird by up to 80 million years." Going back to 1997, Novas and Puerta announced the discovery of Unenlagia (Feduccia 1999), a theropod later hailed as "a missing link," but dated at 90 Ma, about the same age of Deinonychus, that is, some 60 my after Archaeopteryx. Many examples exists, but the point is that the group of theropods thought to be avian ancestors is strictly a Cretaceous radiation, and of more concern, they become more and more birdlike as one approaches the latest Cretaceous. This is also true of certain relatives of the dromaeosaurs, the superficially birdlike troodontids, for which there is now a fragmentary fossil (if correctly identified; Xu et al. 2002) from the Chinese deposits dating to some 128 Ma (if the date is correct). It is worth noting that the specimen described, Sint-mentor, is a "basal troodontid;" that is, an ancestral troodontid present in the late part of the early Cretaceous, and the same is true of the Chinese dromaesaurs. This is further confirmation of the fact that the dromaeosaur (troodontid) radiation was a Cretaceous event.

Prum's (2002) assertion that we have ignored fragmentary fossils of dromaeosaurs from the Late Jurassic is misleading because no credible paleontologist has considered the fragments of a distal radius and femur from the Morrison Formation as anything other than unidentifiable trash. Jensen's Jurassic "birds" (Feduccia 1999) were more or less dismissed at the time of their discovery in 1978. It might be added that small fossils (primarily tibiotarsi) of similar age, taken from the famous African Tendaguru site (that yielded Brachiosaurus), were once thought to be avian, but were later described as "avian-like tibiotarsi of pterodactyloids ... from the Upper Jurassic." (Galton 1980). These are truly amazing fossils, for if these tibiotarsi were discovered in deposits of Eocene age, they would certainly be identified as belonging to some unusual bird.