Are current critiques of the theropod origin of birds science? Rebuttal to Feduccia (2002)

IN MY Perspectives in Ornithology essay (Prum 2002), I advocated that all ornithologists should be excited about research on the theropod origin of birds. Although I did address some criticisms of the theropod hypothesis, I spent most of the essay outlining the data in support of the theropod origin and, most exciting to me, describing the new directions in evolutionary ornithological research that have opened up as a consequence. I concluded that one of the most important frontiers in ornithological research in this century will be the establishment of a thorough scientific understanding of the evolution of avian biology in light of the theropod origin of birds. From nesting biology and physiology to behavior and locomotion, the rewards of studying ornithology as extant dinosaur biology are only just beginning to be reaped (Prum 2002).

In his critique of my essay, A. Feduccia (2002) reviewed much of his previous work but also sprang a new, surprise ending. In summary, he hypothesized that birds evolved from an unknown lineage of early basal archosaurs, and that rampant convergent evolution renders the many derived morphological characters shared by birds and theropods unreliable. However, Feduccia can no longer deny the conclusive evidence that basal dromaeosaurs had feathers (Xu et al. 1999, 2000, 2001, 2003; Czerkas et al. 2002; Norell et al. 2002). In the end, he concedes that dromaeosaurs had feathers. In a rhetorical tour de force that conflicts with decades of his own work and most of his commentary, Feduccia (2002) then hypothesizes that dromaeosaurs are birds, but that the birds, now including the dromaeosaurs, still originated from some unknown early archosaurian ancestor and are unrelated to theropod dinosaurs.

Rather than specifically counter the problems with his commentary, I think it would be most productive to focus my response on the intellectual framework of Feduccia's critique of the theropod origin of birds. Specifically, I will ask the question, "Is this science?" Or is it merely a form of rhetoric designed support an a priori belief about evolutionary process and history?

THE INTELLECTUAL STRUCTURE OF FEDUCCIA'S CRITIQUE

A critical element of science is falsifiability. To be scientific, a hypothesis must be falsifiable and yield predictions that are objectively testable. In a historical science like evolutionary biology, such tests cannot be conducted experimentally. However, we can analyze available evidence with objective repeatable methods. Another critical feature of science is the proposal of alternative hypotheses or theories that attempt to explain the scientific data at hand. Does Feduccia's critique meet these minimal criteria of science?

Feduccia (2002) offers an alternative to the theropod hypothesis of bird origins that is so vague as to be literally untestable. When Heilmann (1926) first proposed the basal archosaur hypothesis of avian origins, he described it optimistically as "wholly without short comings." Similarly, Feduccia (2002) describes his hypothesized early ancestral archosaurian lineage as having "less specialized anatomical baggage" than theropod dinosaurs. This ancestral tabula rasa hypothesis has survived the intervening 75 years between them only because it is permanently immune to falsification. Any potential character conflicts between birds and any known archosaurs can be rejected as irrelevant because the specific organisms can be claimend to not actually represent the yet unknown, hypothetical ancestor that perfectly conforms to the theory. Feduccia's advocacy of an unfalsifiable alternative hypothesis violates a fundamental tenet of science, but it also permits him to continue his permanent rhetorical battle against the theropod hypothesis of avian origin.

In response to my request for an explicit alternative hypothesis of avian origin, Feduccia (2002) concluded that "there are times when there is insufficient evidence to make the formulation of a hypothesis feasible." Here, he is not actually engaged in the search for a scientific solution to the question of avian origins. Essentially, Feduccia concedes that he would rather not do science (i.e. formulate and test alternative hypotheses with data) than to accept the theropod origin of birds. Unfortunately, Feduccia's rejection of the theropod hypothesis and advocacy of an untestable alternative does not constitute a scientific explanation of the origin of birds.

Feduccia (2002) also claims that "phylogenetic systematics stands alone among the sciences" in demanding that critics propose a testable alternative hypothesis. But, as Thomas Kuhn (1970:77) wrote, "The decision to reject one paradigm is always simultaneously the decision to accept another, and the judgment leading to that decision involves the comparison of both paradigms with nature and with each other." What Feduccia rejects as the irrational demands of phylogenetic zealots are actually the baseline requirements of all sciences, from astrophysics to zoology.