Re: Bipedalism

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-03-30 19:13:22 EST, rjmeyer@ix.netcom.com writes:

<< Let me clarify, that when I say "dawn theropod" I am talking about critters
like Eoraptor and it's ancestors.  If I understand the theory correctly, BCF
applies to theropods that lived considerably after Eoraptor died out
(Protoavis being a benchmark).  Or, does BCF apply even to the most
"primitive" of theropods?>>

Yes, BCF applies even to the most "primitive" theropods. They are simply among
the earliest-known ground-dwelling descendants of small, presumably arboreal
forms. The important event was when the rear locomotor system of the arboreal
forms decoupled from the front locomotor system (perhaps so the forelimbs
would be better for climbing, grasping, etc.; who knows?). This freed the
forelimbs to eventually become wings (through what stages we can only guess)
and put the primary burden on the hind limbs of carrying the animal when (for
example) grounded. This transitional event occurred shortly after the time the
theropodomorphs and the phytodinosaurs diverged from the dinosaurian last
common ancestor. The phytodinosaurs are right on the borderline of
bipedality--so that some (brontosaurs, certain ornithischians) were able to
regain quadrupedality, but (known) theropods didn't.
 
<< Then, is bipedalism simply a feature of an arboreal lifestyle? >>

No, not a feature of it, but in the case of theropods, an expectable result of
it. Many of the relatively few extant bipedal vertebrates that are not birds
(such as ourselves) seem to have had arboreal ancestors.