Wednesday, March 01, 2006

T-rex ancestor 'feathered'?

Another older news item from my backlog. My comments are bold and in square brackets.

T-rex ancestor 'feathered', The Australian, Leigh Dayton, February 09, 2006 ... MACHO meat-eating Tyrannosaurus rex had a feathery forefather, which sported a delicate crest on its snout and long slender arms. This smaller and comparatively dandyish ancestor of fearsome T-rex was discovered in the badlands of Xinjiang in far-western China where it lived in the Late Jurassic period, about 160 million years ago. "It was a very spectacular animal," said paleontologist Steve Salisbury, of the University of Queensland in Brisbane. The new dinosaur had a mix of primitive characteristics - like three-fingered hands and blade-like teeth on the sides of its jaw - and more modern T-rex traits such as U-shaped teeth in the front of its upper jaw. The huge "nasal crest" on the dinosaur's nose was a surprise to the discovery team of Chinese, Canadian and US researchers, led by Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. They speculate today in the journal Nature that it may have been a cumbersome sexual ornament, similar to the peacock's tail and the elk's antlers. Because the 3m-long dinosaur - named Guanlong wucaii , or "crowned dragon of the five-coloured rocks - and a more recent member of the same lineage, Dilong, apparently had primitive feathers, Dr Salisbury suggested another surprise: that T-rex may also have had a spot of plumage. "It may have had immature feathers, protofeathers, when it was young," said Dr Salisbury. He added that some sort of feathered covering was probably a characteristic of all coelurosaurs, a group of swift small-bodied creatures that were ancestral to several groups of bipedal three-toed animals, including birds and the Tyrannosauridae, T-rex and its kin. ... [Having followed this "feathered dinosaur" issue from the beginning in 1998, and accepting since 1995 that birds share a common ancestor with reptiles (and therefore possibly, but not necessarily dinosaurs), I have all along considered to be a `groupthink' delusion that the Chinese "feathered dinosaurs" upon which this whole paradigm is based, had true feathers.

There has always been a minority of eminent dissenters, like the leading ornithologist Alan Feduccia who have seen these fosssil "feathers" first-hand and up-close, and yet rejected them as not true feathers, declaring "Feathered dinosaurs ... a myth":

"In 1975 the late Jurassic bird Archaeopteryx was an earthbound, predatory, feathered dinosaur that could not fly. According to the dogma of the time, hot-blooded dinosaurs developed feathers to trap heat, and their wing feathers elongated as insect traps. Since then, however, the evidence for hot-blooded dinosaurs has been dismantled and Archaeopteryx has been shown to be a bird in the modern sense, with fully developed elliptical wings similar to modern woodland birds, and asymmetric flight feathers that form individual airfoils, a flight scapula/coracoid arrangement, and a reserved hallux, found only in perching birds, and known in no dinosaur. Too, as new specimens emerged, the creature has been shown to be more and more birdlike. As cladistic evidence for a dinosaurian origin of birds increased, other feathered dinosaurs (artistic inventions) have emerged, including feathered Coelophysis, Deinonychus, and more recently Unenlagia and Velociraptor; however, there has never been any evidence for these assertions. Most recently, feathered dinosaurs began to emerge from China. First was the downy dinosaur Sinosauropteryx, a rather typical compsognathoid with a line of filaform structures on the middorsal line. Of concern, however, is that down is a secondary adaptation in modern neonate birds and would be maladaptive in a terrestrial dinosaur; downy baby ostriches, when wet, will die from hypothermia unless they seek the shelter of the mother's wings. Today there is no doubt that these structures are not down or feathers but collagen fibers that support a frill or skin flap running along the back. However, after Sinosauropteryx, an article in Nature [Ji, Q., Currie, P.J., Norell, M.A. & Ji, S-A., "Two feathered dinosaurs from northeastern China," Nature, 25 June 1998, Vol. 393, p.753] announced the discovery of two additional feathered dinosaurs from China, named Protarchaeopteryx and Caudipteryx. A cladistic analysis using some 90 anatomical features showed these creatures to be more primitive than Archaeopteryx and therefore feathered dinosaurs. However, the specimens are some 15 to 30 million years younger than Archaeopteryx; half of the characters are primitive and should therefore not have been used, and half of the characters are not present in the fossils, thus leaving two to three skull characters that cannot be ascertained in the crushed specimen. Interestingly, the entire cladogram is rooted in the latest Cretaceous Velociraptor, which occurs some 80 million years after the earliest known bird. Indeed, Caudipteryx shows a suite of features that show it to be a secondarily flightless bird, a Mesozoic kiwi, including a protopygostyle (fused tail vertebrae), an avian occiput, reduced fibula, wing feathers attached as in archaic birds, etc. Finally, there are now excellent specimens of theropod skin, one even showing muscle fibers, and not one shows signs of anything but typical thick tuberculated reptilian skin. Feathered dinosaurs remain a myth." (Feduccia A., "1,2,3 = 2,3,4: Accommodating the cladogram," Proceedings of the National Academy of Sciences USA, Vol. 96, Issue 9, 4740-4742, April 27, 1999)

It is now evident the `feathered dinosaur' paradigm is degenerating, with vague and meaningless statements like, "immature feathers, protofeathers" and "some sort of feathered covering," being "probably a characteristic of all coelurosaurs." That some dinosaurs had an integument made up of fibrous scales does not mean they were feathers or even "protofeathers" (whatever that means)!]

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

No comments: