Commentary The Auk 120(2):550–561, 2003 ARE CURRENT CRITIQUES OF THE THEROPOD ORIGIN OF BIRDS SCIENCE? REBUTTAL TO FEDUCCIA (2002) RICHARD O. PRUM1 Department of Ecology and Evolutionary Biology, and Natural History Museum, University of Kansas, Lawrence, Kansas 66045, USA INMYPerspectives in Ornithology essay (Prum unknown early archosaurian ancestor and are 2002), I advocated that all ornithologists should unrelated to theropod dinosaurs. be excited about research on the theropod origin Rather than specifi cally counter the problems of birds. Although I did address some criticisms with his commentary, I think it would be most of the theropod hypothesis, I spent most of the productive to focus my response on the intel- essay outlining the data in support of the thero- lectual framework of Feduccia’s critique of the pod origin and, most exciting to me, describing theropod origin of birds. Specifi cally, I will ask the new directions in evolutionary ornithological the question, “Is this science?” Or is it merely research that have opened up as a consequence. a form of rhetoric designed support an a priori I concluded that one of the most important fron- belief about evolutionary process and history? tiers in ornithological research in this century will be the establishment of a thorough scientifi c THE INTELLECTUAL STRUCTURE OF understanding of the evolution of avian biology FEDUCCIA’S CRITIQUE in light of the theropod origin of birds. From nesting biology and physiology to behavior and A critical element of science is falsifi ability. locomotion, the rewards of studying ornithol- To be scientifi c, a hypothesis must be falsifi able ogy as extant dinosaur biology are only just and yield predictions that are objectively test- beginning to be reaped (Prum 2002). able. In a historical science like evolutionary In his critique of my essay, A. Feduccia (2002) biology, such tests cannot be conducted experi- reviewed much of his previous work but also mentally. However, we can analyze available sprang a new, surprise ending. In summary, evidence with objective repeatable methods. he hypothesized that birds evolved from an Another critical feature of science is the pro- unknown lineage of early basal archosaurs, and posal of alternative hypotheses or theories that that rampant convergent evolution renders the attempt to explain the scientifi c data at hand. many derived morphological characters shared Does Feduccia’s critique meet these minimal by birds and theropods unreliable. However, criteria of science? Feduccia can no longer deny the conclusive evi- Feduccia (2002) offers an alternative to the the- dence that basal dromaeosaurs had feathers (Xu ropod hypothesis of bird origins that is so vague et al. 1999, 2000, 2001, 2003; Czerkas et al. 2002; as to be literally untestable. When Heilmann Norell et al. 2002). In the end, he concedes that (1926) fi rst proposed the basal archosaur hypoth- dromaeosaurs had feathers. In a rhetorical tour esis of avian origins, he described it optimistical- de force that confl icts with decades of his own ly as “wholly without short comings.” Similarly, work and most of his commentary, Feduccia Feduccia (2002) describes his hypothesized early (2002) then hypothesizes that dromaeosaurs ancestral archosaurian lineage as having “less are birds, but that the birds, now including specialized anatomical baggage” than theropod the dromaeosaurs, still originated from some dinosaurs. This ancestral tabula rasa hypothesis has survived the intervening 75 years between them only because it is permanently immune 1 E-mail: [email protected] to falsifi cation. Any potential character confl icts 550 April 2003] Commentary 551 between birds and any known archosaurs can be to avoid dealing with the overwhelming volume rejected as irrelevant because the specifi c organ- of character evidence from all parts of the body isms can be claimend to not actually represent supporting the theropod origin. He frequently the yet unknown, hypothetical ancestor that argues both sides of the same issue wherever perfectly conforms to the theory. Feduccia’s ad- it is convenient. For example, when the fi rst vocacy of an unfalsifi able alternative hypothesis nonavian theropod furcula was described for violates a fundamental tenet of science, but it Velociraptor (Norell et al. 1998), Feduccia and also permits him to continue his permanent rhe- Martin (1998) claimed that the presence of a fur- torical battle against the theropod hypothesis of cula in the basal archosauromorph Longisquama avian origin. demonstrates that those structures have evolved In response to my request for an explicit al- multiple times in archosaurs and are “weak ternative hypothesis of avian origin, Feduccia evidence” of phylogenetic relationship. Now, (2002) concluded that “there are times when applying his “character by character” approach there is insuffi cient evidence to make the for- in this commentary, Feduccia mentions that the mulation of a hypothesis feasible.” Here, he is furcula of Longisquama in an effort to support the not actually engaged in the search for a scien- hypothesis that Longisquama is closely related to tifi c solution to the question of avian origins. birds, in direct contradiction to his earlier pub- Essentially, Feduccia concedes that he would lished conclusions. Simultaneously, he ignores rather not do science (i.e. formulate and test the discoveries since 1998 of furculae or paired alternative hypotheses with data) than to accept clavicles in six to nine major lineages of theropod the theropod origin of birds. Unfortunately, dinosaurs, including dromaeosaurs, ovirap- Feduccia’s rejection of the theropod hypothesis tors, tyrannosaurs, allosaurs, and coelophysids and advocacy of an untestable alternative does (Tykoski et al. 2002). Of course, the only scientifi c not constitute a scientifi c explanation of the ori- way to resolve alternative hypotheses of charac- gin of birds. ter evolution and character confl icts are by ap- Feduccia (2002) also claims that “phylogenet- plying a repeatable, explicit, analytical method ic systematics stands alone among the sciences” to reconstruct evolutionary history of characters in demanding that critics propose a testable and organisms. But Feduccia (2002) openly re- alternative hypothesis. But, as Thomas Kuhn jects available systematics methods as forcing (1970:77) wrote, “The decision to reject one “into algorithmic form what is arguably the most paradigm is always simultaneously the decision subjective and qualitative fi eld of biology.” to accept another, and the judgment leading to Feduccia’s (2002) dogmatic belief in ram- that decision involves the comparison of both pant evolutionary convergence in morphology paradigms with nature and with each other.” literally begs the question—that is, presumes What Feduccia rejects as the irrational demands exactly the facts that need to be demonstrated. of phylogenetic zealots are actually the baseline The only way to demonstrate convergence is to requirements of all sciences, from astrophysics show that the majority of character evidence to zoology. supports a hypothesis of phylogeny in which Because Feduccia’s scenario is untestably the convergent characters are shown to have vague, he is reduced exclusively to criticizing the evolved independently (Patterson 1982, Pinna theropod hypothesis. Feduccia (2002) portrayed 1991). Yet, Feduccia rejects both repeatable the theropod origin of birds as a vast cladisitic systematic methods and explicit, testable al- conspiracy to deceive the ornithological com- ternative hypotheses, making it impossible for munity. Like a conspiracy theorist, he unerringly him to demonstrate the convergence in which interprets evidence—even the new, ultimate he believes. Feduccia (1999a,b; 2002) repeatedly evidence of feathered theropods—as favoring cited his favorite examples of failed phyloge- his preconceived conclusions. Feduccia (2002) netic hypotheses as a justifi cation for rejecting argues that hypotheses of character homology repeatable scientifi c methods, but he failed to cannot be tested by congruence with other char- mention that it was subsequent phylogenetic acters, advocating a character by character ap- analyses that established the preferred hypoth- proach instead. This ad hoc method permits him eses. Actually, the repeatable scientifi c methods to interpret each separate character in whatever that Feduccia rejects are the solution, not the manner he prefers to support his argument, and problem. Feduccia (2002) further states that 552 Commentary [Auk, Vol. 120 the theropod hypothesis implies that drom- tion of the temporal paradox by two thirds (Xu aeosaurs are “avian ancestors,” and that bird et al. 1999, 2000, 2001, 2003; Czerkas et al. 2002; are “derived from dromaeosaurs,” when it is Norell et al. 2002), bird-like nesting behavior in well known that the hypothesis states that the theropods (reviewed in Prum 2002), and most birds and dromaeosaurs (probably including recently by four winged dromaeosaurs (Xu et al. troodontids) are sister groups. 2003). Given that the theropod origin of birds is Feduccia has long maintained that the 80 Ma entirely consistent with and supported by all of “temporal paradox”—the temporal gap in fos- the new evidence discovered in the last decade, sil record between the earliest bird fossils and and that many testable predictions generated the earliest fossils of the proposed avian sister by the hypothesis have been independently taxon (dromaeosaurs and troodontids)—was a supported, it is an overwhelmingly