Bird bipedalism (was A layman's question...)

Thomas R. Holtz, Jr. (
2 Jul 1996 12:24:41 GMT (ORDOVER) wrote:

> Here's a question -- were birds bipedal before they could fly? Bats
> aren't bipedal; neither are flying squirrels. Why are birds?

Birds were bipedal becuase their ancestors, coelurosaurian theropod
dinosaurs, had been bipedal for several tens of millions of years before
the advent of bird flight. All fossil birds show a fully upright
posture of the hind legs, unlike the condition (as you note) found
in bats, flying squirrels, and also dermopterans (flying "lemurs"),
flying marsupials, flying lizards, flying frogs, etc.

This has been one of the primary pieces of evidence that birds did
not go through a flying squirrel-like gliding stage in their evolution.