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"Flight theory has legs"


I'm not quite convinced. I wonder if Chris examined the hand-claws of theropods. After all, sinornithosaurs, microraptors and archaeopterygians had *four* limbs to climb trees with.


"Flight theory has legs"

By Greg Roberts
July 11 2003

The question of how birds learned to fly has long puzzled the experts. Anatomists and palaeontologists have generally favoured the "top down" theory - that some time during the Jurassic period before about 150 million years ago, dinosaurs clambered up trees and eventually, after developing feathers and bristles and learning to glide to the ground, the art of flying somehow evolved.

Now, it seems, the "bottom up" theory has more feathers to fly with.

A study on the claws of birds suggests their forebears were much more terrestrial, or ground-dwelling, than had been thought, and that they had their feet very much on the ground before taking off.

In the first major study of its kind, Chris Glen, for his doctoral thesis at the University of Queensland, has studied the claws of 1500 modern-day birds from 500 species and compared them with the fossils of long-extinct "dino-birds".

In a paper delivered to a national conference of palaeontologists at the Queensland Museum in Brisbane this week, Mr Glen explained that the curvature of the modern birds' claws varies radically and relates directly to the extent to which birds spend time on the ground.

At one end of the spectrum, the claws of woodpeckers, which vigorously climb tree trunks, curve 170 degrees. At the other end, the claw of the flat-footed jacana, a lily-trotting waterbird, curves barely at all.

"In between, and including all the perching birds we're so familiar with, you have the full range," Mr Glen said outside the conference.

When he checked the fossil records of the ancestors of birds that lived between 120 million and 150 million years ago, he was surprised by the extent to which they matched the claws of the flat-footed birds.

For instance, the sinornithosaurus was a two-legged beast - there has long been debate about whether many dinosaurs were reptiles, birds or something in between - about 1.5 metres tall that hunted in packs. (They are the mean-looking critters continually trying to make a meal out of Sam Neill in Jurassic Park.)

The sinornithosaurus had been suspected of having tree-climbing capabilities but Mr Glen said its claws indicate this is not so.

Other dino-birds known to be capable of flight, such as the starling-sized confuciusornis of China and Europe's magpie-sized archaeopteryx, were thought to be arboreal.

But Mr Glen said the claws of most suggest they were more likely to be terrestrial, probably behaving similarly to modern-day chickens or ground pigeons, which fly reluctantly.

Only one of the flight-capable dino-birds he examined, the sinornis of China, appears to have been primarily arboreal.

"The evidence is quite clear that most of these bird ancestors were ground-dwellers," Mr Glen said. He said the tree theory - that birds "used the height of the tree and so on to advantage to gradually develop a flying capability" - had made a lot of sense. "However, it appears more likely now that it was a case of from the ground up."

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