Birds are extant dinosaurs; it's a phrase that (while initially quite stimulating) has been expressed so often that it borders on being trite. There are dozens of technical papers, popular books, collections of scholarly essays, and feathered dinosaur toys to drive the point home, but I've often been led to wonder what ornithologists make of all this. Paleontologists have been the main architects that have strengthened the connection between dinosaurs and birds in recent years, but given that fossil finds have such important implications for the origin and evolution of birds I'm a bit puzzled as to why ornithologists are relatively silent about this issue. Perhaps even more surprising, there seems to be some amount of resistance to the idea that dinosaurs are the ancestors of birds; it was strange to read Ernst Mayr dismiss the dinosaur-bird link in his book What Evolution Is in favor of a "thecodont" ancestry for birds like that of Heilmann (although Heilmann admitted that dinosaurs were exceedingly close to birds; the fact that the furcla of dinosaurs were not known during his time resulted in him advocating a "pseudosuchian" ancestry for birds over dinosaurs). Some ornithologists have recognized the importance of recent paleontological research to their discipline though, as outlined by Richard Prum in a 2002 paper that appeared in the journal The Auk.
Certainly there are ornithologists interested in what the fossil record has to say about bird origins and the relationship between birds and dinosaurs, but as Prum points out, most papers about the evolution of birds are found in the paleontological literature. I'm not an ornithologist so I don't know if there has been a sudden influx of papers talking about the recent fossil material of early birds and their relatives, but as of 2002 there only seemed to be one paper (Zhou's refutation of Mononykus as a bird in The Auk) involving dinosaurs in the ornithological literature. Prum believes this disjunct is the result of two main factors;
First, most ornithologists have not become familiar enough with the primary literature describing the various characters to consider the evidence for themselves. Further, few ornithologists have formal paleontological training, and some may have relied on the criticism of a few to form the opinion that the evidence supporting the theropod hypothesis is flawed. The second reason is that many ornithologists are satisfied that the issue is irrelevant to their research and teaching. Like many natural historians over many centuries, ornithologists are generally convinced of the peculiar uniqueness of birds, because we gain our professional identities as ''ornithologists'' from it. Focusing on the apparent uniqueness of birds may reinforce our professional identities or self esteem, but it may not help us do the best possible ornithological research and teaching.
The second factor might be the more influential of the two; paleontologists working on theropod dinosaurs seem to have a greater appreciation for the relationship between birds and dinosaurs than many ornithologists do, many of whom seem to have more of a "grade" perspective (looking at living birds, the ancestry of the derived avians not being relevant even if it is mildly interesting). Again, though, I must be cautious here; I do not know the field of ornithology well enough to effectively gauge general feelings on this topic even if the lack of discussion about bird origins is puzzling.
As more is understood about dinosaurs and their paleobiology, the implications for ornithology are intensified. Questions about homeothermy, metabolic rates, the origin of feathers, the origin of flight, adaptation of the skeleton to hold air sacs, the origin of brooding behaviors, growth rates, reproduction, development, and other issues are all irrevocably tied to research being carried out in the paleontological realm. Answers to these questions cannot be derived from the fossil record alone, but in my lifetime there has been an explosion of discoveries that one would think would be of great interest to ornithologists. Given the importance of collaboration between ornithologists and paleontologists in the future, Prum makes a few suggestions as to how the gap between the fossil record and studies of modern birds can be narrowed;
How can ornithologists participate? First, the theropod origin of birds and general dinosaur biology should be taught in all introductory ornithology courses. The Encyclopedia of Dinosaurs (Currie and Padian 1997) is an excellent place to start for supplemental material. (Interested ornithologists can also contact the author for sample lecture notes.) Basic dinosaur biology and the theropod origin of birds should be incorporated in all future ornithology textbooks: there is not a single chapter of a standard ornithological text that could not include additional insights on avian biology based on their theropod origin. But textbooks are based on the scientific literature. It will be important for ornithologists to become broadly familiar with dinosaur diversity and apply their knowledge of birds to the larger field of dinosaur and archosaur biology. Ornithologists should develop research partnerships with dinosaur paleontologists, and paleontological papers on nonavian dinosaur biology with implications for ornithology should be published in ornithological journals. There are now many examples of research that bridges the narrowing gap between birds and other dinosaurs and genuinely contribute to ornithological knowledge (e.g. Gatesy and Middleton 1997; Wagner and Gauthier 1999; Hutchinson 2000a, b).
Until any credible alternative is proposed, it is time to abandon debate on the theropod origin of birds, and to proceed to investigate all aspects of the biology of birds in light of their theropod origin. This fertile frontier of knowledge promises to be among the most exciting developments in ornithology in the coming century, and ornithologists should be actively interested in and participating in this field. The time has come for our discipline to realize that ornithology is extant dinosaur biology. Ornithology can only profit as a result.
I admire Prum's call for increased collaboration and for an evolutionary view of ornithology rather than just focusing on modern or recent species, but I am sad to say that his paper seems to have fallen on deaf ears. I may be wrong, but as far as I have been able to tell from a few web searches for publications the only mentions of dinosaurs in ornithological journals have been weakly or strongly critical of the theropod origin for birds. The strongest opposition comes from figures like Larry Martin and Alan Feduccia, but there is also an vague fog of skepticism that is not fully expounded upon (and no reasonable alternatives to the theropod ancestry for birds are proposed). An example of the weaker form of resistance is illustrated in a 2005 review of Feathered Dragons that appeared in The Auk. The authors of the review, Frances C. James and John A. Pourtless IV, use the review to caution ornithologists against being taken in by the "heady" hypotheses of paleontologists;
Most authors in this book have taken the birds-are-dinosaurs paradigm as a given, dismissing alternatives in Kuhnian fashion, but ornithologists should be more cautious. They know that 35 families of modern birds include taxa that are flightless, and that flightless birds can get very large. At least one group of "dinosaurs," the oviraptorosaurs, is now recognized as flightless birds (Lü 2000, Maryanska et al. 2002). No wonder they have birdlike eggshells and brooding behavior! If several different groups of early birds evolved flightlessness, deciphering the origin of birds from the fossil evidence is going to require more ornithological expertise and skepticism than is apparent in this book or several other recent books on this subject. Some of the papers here are not relevant to ornithology. Others may be more relevant to ornithology than their authors thought.
The assertion that members of the Oviraptorosauria are flightless birds is incorrect; they are still dinosaurs, although (as the authors sarcastically note) they share a number of traits with birds as do other members of the Maniraptora. This error aside, the question is still open as to why "ornithological expertise and skepticism" has not been forthcoming on the issue of the evolution of birds from dinosaurs. The only other literature readily available involving dinosaurs and birds was (like the review that inspired this post) by Richard Prum or Alan Feduccia in The Auk. Prum's second paper, entitled "Are Current Critiques of the Theropod Origin of Birds Science? Rebuttal to Feduccia (2002)," addresses a critique to Prum's first paper (mentioned above) by Alan Feduccia, Prum justly criticizing Feduccia's hypothesis that birds arose from some unknown basal archosaur and that dromeosaurs are actually birds. Indeed, in Feduccia's scheme dromeosaurs would be flightless birds only distantly related to other dinosaurs, a hypothesis that is thoroughly refuted by the tons of fossil evidence that have come to light to date. As Prum notes, Feduccia's claim requires convergent evolution run wild, perhaps even to a teleological extent given the shared derived characters shared between dromeosaurs and birds, and there's no reason to take such claims seriously.
The disinterest of the ornithological community in the origin and ancestry of birds is unfortunate, but I do not see how it can last. Any general understanding of birds is going to eventually require at least the recognition that they evolved from dinosaurs and many of the traits we consider to be hallmarks of birds are much older than previously thought. To reiterate Prum's sentiments, "The time has come ... to realize that ornithology is extant dinosaur biology."
References;
James, F.C.; Pourtless, J.A. IV. (2005) "Feathered Dragons: Studies on the Transition from Dinosaurs to Birds." The Auk, Vol. 122, (2), pp. 714-716
Prum, R.O. (2002) "Why Ornithologists Should Care About the Theropod Origin of Birds." The Auk Vol. 119 (1), pp. 1-17
Prum, R.O. (2003) "Are Current Critiques of the Theropod Origin of Birds Science? Rebuttal to Feduccia (2002)." The Auk, Vol. 120 (2), pp. 550-561
Zhou, Z. (1995) "Is Mononykus a Bird?" The Auk, Vol. 112 (4), pp. 958-963
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I have wondered at length about why ornithologists are resistant to the theropod origin of birds. Perhaps they feel like paleontologists are "butting in" on their territory. I'm really not sure--I don't know any ornithologists. And the truth is that modern birds are an incredibly unique group of dinosaurs APART from their non-avian forebearers. A theropod ancestry for birds does not somehow overshadow the uniqueness of birds. Indeed, birds are probably more successful (in terms of biodiversity) than the whole of the non-avian Dinosauria!
I agree that ornithology textbooks need to focus a bit more on the theropod origins of birds, though. I have an ornithology textbook for restoration purposes, and I'm happy to report that there is a chapter about theropods and birds.
I don't think it's anything particular to Ornithology. Look at the fights paleontologists and molecular biologists are having over which cladistic trees are in fact valid for different families. Not just based upon dates of divergence, where molecular calibration may indeed be off, but even resistance to clades like Afrotheria that are pretty much airtight now genetically, but lack the transitional fossils "prove" such a hypothesis morphologically.
It's found throughout the academy. Neoclassical economists think virtually everything humans do can be boiled down to individuals acting in self interest. Psychologists look for individual pathologies causing societal ills, sociologists group pathologies. Behavioral geneticists find self-interested genes behind virtually every human activity. Quantum physicists suggest that human consciousness may have a quantum basis rather than simply a chemical one. And postmodernists/poststructuralists can discount every theory because when deconstructed, personal and society-wide agendas can be seen as underpinning it.
I think two things play into all this academic craziness. One is the simple turf-war idea. The academy makes people become hyper specialized instead of rounded academics, and I think, in response, a good deal of academics become extremely defensive of "their bit" of the cognating noosphere. This results in feeling personally threatened if their intellectual turf is broached by those with "no background," and conversely wanting to pour their knowledge into as broad a subject as possible - hopefully a "theory of everything" of some sort.
The second part is deeper, and has to do with humans being at base irrational animals. Science is neutral, but scientists and other academics are not. And academic training does take on elements of faith unfortunately. Going back to my first example, a paleontologist is trained to think "bones don't lie," so their first instinct, if a genetic study shows two groups with very similar morphology are in fact not very close, is to question the molecular study. Of course, at least some doubt in all initial studies is warranted before additional studies confirm the findings, but the initial doubt is in part caused by an article of faith for paleontologists - bones beat genes. Most scientists overcome this, but all fields have these implicit faith-based assumptions underlying them.