Thursday, 17 January 2013

Let me see you shake your tail feather

We've known for some time now that dinosaurs had feathers and that the theropod dinosaurs were the ancestors of modern birds. The proof is quite overwhelming - particularly the large number of feathered dinosaur fossils found in recent years in China. And then, last year, the first dino-feathers trapped in amber were discovered near Grassy Lake in Alberta - dating from the Late Cretaceous period. And they told a fascinating story.

"We're finding two ends of the evolutionary development that had been proposed for feathers trapped in the same amber deposit," said Ryan McKellar of the University of Alberta. The team's find confirms that individual filaments progressed to tufts of filaments from a single origin, called barbs. In later development, some of these barbs can coalesce into a central branch called a rachis. As the structure develops further, further branches of filments form from the rachis. "We've got feathers that look to be little filamentous hair-like feathers, we've got the same filaments bound together in clumps, and then we've got a series that are for all intents and purposes identical to modern feathers," says Mr McKellar. "We're catching some that look to be dinosaur feathers and another set that are pretty much dead ringers for modern birds."

We also now know that feathers appeared much earlier in dinosaur evolution than first thought. Fossils of Ornithomimus edmontonicus - which looked something like ostriches but were not previously known to have feathers - have recently been found to have hundreds of traces of filaments along the body and limbs. Moreover, as the team reported in Science, while one of the two adult skeletons showed evidence of possessing a pennibrachium = a forelimb bearing long feathers that form a winglike surface - the third specimen, a juvenile dinosaur about 1-year-old, lacked this structure, although it still had numerous feathers along its body. This marks the first time that wings and feathers have been identified in ornithomimosaurs. "Our specimens are currently the most primitive dinosaur to show winglike structures," says Dr Darla Zelenitsky, a geoscientist at the University of Calgary in Canada, "And because ornithomimosaurs were fairly large, weighing 150 kilograms or more, these earliest wings did not initially evolve for flight - they were obviously not flyers or gliders. Moreover, O. edmontonicus does not appear to have developed its full plumage until it reached the adult stage, which suggests that the wings and feathers served some sort of adult reproductive function such as courtship and brooding."

Meanwhile, another study of a 150 million year old dinosaur fossil has revealed it had multi-coloured feathers. The research, published in the journal Science, compared the structures which determine colour in living bird feathers with those in the fossil. "This would be a very striking animal if it was alive today," said Yale University's Professor Richard Prum, co-author of the report. It is believed the colours would have helped the dinosaur attract a mate. Anchiornis huxleyi is a four-winged dinosaur which lived in the late Jurassic Period in China. Researchers chose this particular fossil to work on because the feathers were so well preserved.

And why shouldn't dinosaurs have been colourful beasts? Just look at modern birds, reptiles and amphibians. But, more than that, look at how dynamic our modern animals are. Doesn't it seem likely that dinosaurs were just as active in their competition, mating and sexual attraction displays?

Well, another recent study suggests proof of exctly that. In an issue of the journal Acta Palaeontologica Polonica, three paleontologists posit that fossilised oviraptors possessed structural features that are characteristic of those found in modern birds with ornamental tails. For example, in the early oviraptor Similicaudipteryx, the last caudal vertebrae (the tip of the “tailbone”) are fused into a structure known as a “pygostyle," which was long thought to be a feature exclusive to modern birds. There is no evidence that Similicaudipteryx was a flying species, and the authors suggest that the bone and muscle structures that can be discerned from the fossil remains are consistent with those seen in birds with tail displays that don't aid in flying but do functional as flashy ornaments, such as peacocks, turkeys, and birds of paradise (note that these birds are not completely flightless, the tails just don't contribute to optimal flight). Some species do indeed favour form over function, and apparently the trend may have started way back in the Mesozoic.

These assertions are, of course, subject to scepticism due to the limitations of the fossil record. This is part of science - publishing new perspectives or conclusions and allowing the scientific community to contribute further analyses and information, ultimately either supporting or discarding the idea. What is unquestionable, however, is that this paper signifies just how far palaeontology has come in recent years. New finds and new technology have yielded broader and deeper information about the details of what dinosaurs actually looked like, how they moved, and how they might have interacted in their ancient world.


BBC News
BBC Science

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