The summer of 2000 promised to be very exciting for ornithologists and paleontologists alike as they flew into Beijing for the fifth quadrennial meeting of the Society of Avian Paleontology and Evolution (Ref 1). The setting was most appropriate given the richness of fossils that have been unearthed in Chinese soil. The central theme of the meeting lay in trying to resolve the question of whether birds had really evolved from dinosaurs (Ref 1). However, rather than a harmonious discussion with the constructive disagreement that one might expect from any scientific ‘get-together’ aimed at resolving discrepancies in data, the meeting did nothing but expose an underlying discord (Ref 1).
While some scientists such as Berkeley’s John Hutchinson and Yale ornithologist Richard Prum were frustrated over issues that they considered long resolved, others were much more skeptical about the certainty of the facts. Storrs Olson, head of ornithology at the National Museum of Natural History, weighed in by accusing Prum of engaging in “ideological mumbo-jumbo” when Prum claimed that feathers had the same evolutionary origin as “hair like integuments found on dinosaur fossils” (Ref 1). So strong was Olson’s feeling against the evolutionary link drawn between birds and dinosaurs that throughout the meeting he and others wore badges stating their case: “BIRDS ARE NOT DINOSAURS” (or B.A.N.D for short; Ref 1). University Of North Carolina paleontologist Alan Feduccia, well known for his discussions on temporal discrepancies between bird and dinosaur fossils, was similarly uncertain about the dinosaur-bird link. Feduccia made his uncertainty public to the sound of accusations claiming a creationist undertone (Ref 1).
With the latest evidence Olson and his ‘BAND of merry men’ appear to have been vindicated. New data on how birds breathe makes the dinosaur-bird link untenable. According to a recent study, the unique thigh bone and muscle structure in birds’ legs play a key role in preventing lung collapse (Ref 2). For birds, that need about twenty times more oxygen than say reptiles, such structural support is crucial to survival (Ref 2). Theropod dinosaurs from which birds are thought to have descended, did not sport such a fixed thigh bone structure and are therefore not viable candidates for a hypothetical bird ancestor (Ref 2).
Of course the impasse over how birds evolved extends well beyond thigh bones and muscles. In fact, the origin of feathers continues to be a formidable stumbling block for ‘evo-philes’. To further understand the difficulty that the feather poses to the assumed evolutionary transition from dinosaurs to birds, consider the feather’s structural foundations. What we know is that the central rachis (or shaft) of the feather branches off into smaller barbs and barbules. The barbules are equipped with tiny hooklets at their ends that interlock with ridges in the posterior barbules to form an impervious, tightly-held vane (Ref 3).
From an aerodynamic standpoint, the arrangement of the feathers in the overall shape of the wing makes for an aerofoil that displays minimal levels of turbulence (Ref 3). The ability to change the geometry and shape of such an aerofoil makes it ideally suited for the various tasks that the bird has to perform such as landing, soaring and flapping. From a molecular and cellular perspective, the story is no less fascinating. The feather follicle, from which the central rachis projects, contains specific zones of epithelial cells specialized in the formation of each of the components of the feather (Ref 4). The molecular mechanisms by which such cell specialization is achieved have also been elucidated in recent years (Ref 4). Through concentration gradients and a highly-regulated activation of specific genes, the morphogenesis and development of a feather is a very tightly-controlled affair (Ref 4).
With such a realization, we begin to get a sense of why it was that twenty three years ago biologist Michael Denton so emphatically decried the step-by-step, unguided evolutionary origin of wings (Ref 3). As Oregon State University Professor John Ruben humorously quipped, “a velociraptor did not just sprout feathers and fly off into the sunset” (Ref 2). The wing- the perfect aerofoil- must meet rigorous criteria before it can provide the necessary lift (Ref 4). No slight fraying of dinosaur scales would have done the job.
Seemingly oblivious of these intractable challenges, some scientists have gone all out to prop up their evolutionary meanderings by focusing on the three-fingered limbs of theropod dinosaurs and modern day birds (Refs 5,6). Paleontologists Xing Xu and James Clark for example recently published on two specimens of a 156 million-old, toothless-beaked, herbivorous theropod called Limusaurus inextricabilis that, they maintain, is a Darwinian-style ‘missing link’ (Refs 5,6).
One factor that has long been a source of consternation is that the finger digits of theropods and birds do not appear to match. While theropods seemingly carried digits 1,2 and 3 of the pentadactyl arrangement, birds display what scientists believe to be digits 2,3 and 4 (Refs 5,6). Xu and Clark have ruffled feathers by claiming that theropod digits have historically been misidentified. Based on their study of L. inextricabilis, they contend that just like in birds early theropods would have had digits 2,3 and 4 (Refs 5,6).
Such a conclusion is not without its critics. In fact prominent Yale evolutionary geneticist Gunter Wagner has questioned the numbering assignments of bird digits adding that bird wings might be based on digits 1,2 and 3 after all (Ref 5). Wagner cites fundamental aspects of embryonic development in support of his case. University of California paleontologist Kevin Padian has similarly suggested that the digit morphology of L. inextricabilis might represent nothing more than an “oddly reduced hand”, commensurate with its herbivorous lifestyle (Ref 5).
Today, nine years after the Beijing meeting, Olson would seemingly be justified in wearing his famous badge. For him and others, the ‘B.A.N.D’ does indeed play on. To be sure, contemporary evidence shows birds to be a distinct phyletic group not easily integrated into a man made evolutionary scheme. While evolutionists point proudly to the apparent anatomical similarities between birds and dinosaurs, they themselves admit to the pressing need to resolve crucial questions about the origin of flight, the evolution of feathers and the conversion to endothermy (Ref 7).
These are not side questions designed to obfuscate discussions, but rather questions that are central to the matter at hand. In light of such facts, perhaps a more radical message needs to be conveyed that echoes the beat of a different mantra: BIRDS ARE REALLY BIRDS (or B.A.R.B for short). It is perhaps time to re-examine our most treasured notions of bird evolution.
Literature Cited
1. Rex Dalton (2000), Feathers fly in Beijing, Nature, Volume 405, p.992
2. See ‘Discovery raises new doubts about dinosaur-bird-links’, http://www.eurekalert.org/pub_releases/2009-06/osu-drn060809.php
3. Michael Denton (1986), Evolution: A Theory in Crisis, Adler and Adler Publishers, Bethesda Maryland, 1st Edition, pp. 202-208
4. Mingke Yu, Ping Wu, Randall B. Widelitz, Cheng-Ming Chuong (2002), The morphogenesis of feathers, Nature, Volume 420, pp.308-312
5. Matt Kaplan (2009), Dinosaur’s digits show how birds got wings, 17 June 2009, Nature, doi:10.1038/news.2009.577
6. Xing Xu, James M. Clark, Jinyou Mo , Jonah Choiniere, Catherine A. Forster, Gregory M. Erickson, David W. E. Hone, Corwin Sullivan, David A. Eberth, Sterling Nesbitt, Qi Zhao, Rene Hernandez, Cheng-kai Jia, Feng-lu Han, Yu Guo (2009), A Jurassic ceratosaur from China helps clarify avian digital homologies, Nature 459, pp.940-944
7. See ‘Are Birds Really Dinosaurs?’, http://www.ucmp.berkeley.edu/diapsids/avians.html