Thursday, March 16, 2006

New fossil complicates picture of feather evolution

New fossil complicates picture of feather evolution, San Diego Union-Tribune/AP, March 15, 2006 NEW YORK - A 150 million-year-old fossil from southern Germany has paleontologists ruffled over how feathers arose in the line of dinosaurs that eventually produced birds. The fossil is a juvenile carnivorous dinosaur about 2 1/2 feet long that paleontologists have named Juravenator for the Jura mountains in southern Germany where it was found. ... The fossil's exceptionally well-preserved bone structure clearly puts it among feathered kin on the dinosaur family tree. Because all of its close relatives are feathered, paleontologists would expect Juravenator to follow suit. But a small patch of skin on Juravenator's tail shows no sign of feathers. And the skin also doesn't have the follicles that are typical of feathered dinosaurs, said Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County. He and Ursula B. Gohlich of the University of Munich describe the fossil in Thursday's issue of the journal Nature. "It has a typical scaly dinosaurian skin," Chiappe said. The paleontologists believe Juravenator's closest known relative may have been a fully feathered dinosaur from China, Sinosauropterix [sic]. There are a number of possible explanations for Juravenator's nakedness. Feathers could have been lost on the evolutionary line leading to Juravenator after arising in an ancestor to both it and its feathered relatives. Or feathers could have evolved more than once in dinosaurs, cropping up in sister species at different times and places. It is also possible that this particular fossil of Juravenator, which appears to be a juvenile, only grew feathers as an adult or lost its feathers for part of the year. But there is another possibility as well, said Mark Norell, curator of paleontology at the American Museum of Natural History: It is entirely possible that Juravenator did have feathers, but they simply failed to fossilize. "Feathers are really just difficult things to preserve," Norell said. To support his hypothesis he pointed out that several fossils of the oldest known bird, archaeopteryx [sic], lack feathers. [See also: "German dino find clouds picture of feather evolution," CBC; "Dinosaur Find Raises Questions about the Origin of Feathers," Livescience; Fossil prompts rethink on dinosaur feathers," MSNBC; "Scaly New Dinosaur Creates Flap Over Feathers' Evolution," National Geographic, etc.

Here we have "a small patch of skin" where feathers would be if this dinosaur had feathers, on a close relative of the claimed `feathered dinosaur' Sinosauropteryx which is claimed to have feathers on its tail, yet "Juravenator's tail shows no sign of feathers"! This is further support for ornithologist Alan Feduccia's theory that "these structures are not down or feathers but collagen fibers that support a frill or skin flap running along the back." Norell (since he is a - if not the - major proponent of the `feathered dinosaur' theory) does not mention yet another possibility, that no dinosaur has feathers, they being the paleontology equivalent of the canals on Mars that eminent 19th/early 20th century astronomers could see with their own eyes (because that is what they wanted to be there)!]

Whether or not the new specimen raises interesting questions about how feathers - and thus birds - evolved, most experts do not see it as a challenge to the widely accepted view that modern birds are descended from dinosaurs. ... [Since I accept universal common ancestry I would have no problem if birds did descent from dinosaurs (although I regard it as more likely that birds shared an earlier reptile common ancestor with dinosaurs). But that is not the issue here, which is whether dinosaurs had true feathers. And this featherless patch of skin on a dinosaur where feathers should be if the `feathered dinosaur' theory was true, is strong (if not conclusive) evidence against that theory.]

Stephen E. Jones, BSc (Biol).
"Problems of Evolution"

"The inconclusiveness of Darwin's argument escaped neither his friends nor his critics. Huxley summed up the matter precisely. `What,' he asked, `does an impartial survey of the positively ascertained truths of paleontology testify in relation to the common doctrines of progressive modification?' To which he frankly replied: `It negatives these doctrines; for it either shows us no evidence of such modification, or demonstrates such modification as has occurred to have been very slight; and, as to the nature of that modification, it yields no evidence whatsoever that the earlier members of any long-continued group were more generalized in structure than the later ones.' [Huxley T.H., "Paleontology and the Doctrine of Evolution," [1870], "Critiques and Addresses," Macmillan: London, 1883, pp.182-83.]" (Himmelfarb G., "Darwin and the Darwinian Revolution," [1959], Elephant Paperbacks: Chicago IL, 1996, reprint, p.332)

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