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Re: caudofemoralis and flight



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. Certainly other
changes did occur in the hindlimb musculature during theropod evolution,
such as reduction of the CFL and shifts in muscle positions correlated with
the retroversion of the pubis, expansion of the iliac blade, etc. Again,
Steve Gatesy's work has already made a strong case for this (although he's
been careful about making statements about which muscles changed and what
the functional consequences were), and earlier work by Perle Altangerel,
Rinchen Barsbold, Romer, Ostrom, etc. have discussed the possible changes
in pelvic limb musculature correlated with osteological changes. Note that
the pubis of developing chick embryos retroverts... (Romer's 1927 Chick
thigh muscle paper).

>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. It's interesting that
ornithischians retroverted the pubis without reducing the fourth trochanter
(in fact, maybe even enlarging it, based on specimens I've seen), though,
but they obviously had some differences in myology and osteology in any
case. Definitely a problem worthy of more investigation, yet not a
hypothesis to compound with hypotheses about the origin of flight in
theropods, IMHO.

                       --John R. Hutchinson