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Re: caudofemoralis and flight



In a message dated 97-07-24 16:36:23 EDT, jrhutch@socrates.berkeley.edu (John
R. Hutchinson) writes:

<<Dinogeorge writes:

>... concomitant strengthening of the
>caudifemoralis musculature certainly didn't hurt theropods' cursorial
>abilities.

AFAIK, the caudofemoralis musculature was not increased in size in
theropods compared to most other Reptilia. How then was it strengthened? I
doubt that the CFL had more force output ("strength") than before;
theropods just inherited a plesiomorphic locomotory module.>>

Perhaps I should have said, "Made more efficient." The muscles themselves
were very probably no stronger than in pre-theropod dinosaurs. But they were
more efficient for walking and running because the hind limb was more erect
and the body was less flexible than in earlier archosaurs, which allowed the
musculature to be used more for walking, running, and moving the tail and
less for simply maintaining body and tail flexure.

<<>Pubic retroversion, however, may simply be related to giving the
>body a more aerodynamic shape, as it occurs in Theropoda only in the most
>avian-like forms.

I don't know how that would work, or if its prevalence in maniraptoriformes
is causally linked to flight at all. The fact that similar changes occur in
therizinosauroid theropods and basal ornithischians seems to hint at a
similar pattern related to locomotion, but it's tough to say without
rigorous biomechanical testing of such hypotheses.>>

"Therizinosauroid theropods"?? What are those?

Since neither segnosaurs nor ornithischians are particularly closely related
to theropods, there is no reason to believe that pubic reversion in those
groups had a similar origin to the pubic reversion of theropods. In pre-avian
theropods, pubic reversion surely helped give the rear and underside of the
body an aerodynamic shape, as it does in virtually all living birds; in
segnosaurs and ornithischians, pubic reversion probably helped to accommodate
the more intricate digestive system that herbivores seem to require. This is
simply an example of convergence of form.