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RE: Velociraptor profiles and a little background



Waylon Rowley wrote:

>      Encephalization Quotient, actually. The volume
> of the brain in relation to body size, in any case.

Yep, I realized what "EQ" meant after I sent the message.  Apparently the
term was coined by a psychiatrist, Harry Jerison, back in the 70's.

> _Troodon_ has something like a ~50 cc brain and they
> say Bambiraptor's brain is relatively larger, though I
> don't have the numbers (maybe someone could help with
> that?). 

Larsson et al. (2000) describe increase in the size of total endocranial
volume (relative to body mass) within Theropoda, with the extra brain volume
invested disproportionately in the forebrain.  The authors suggest that
brain and cerebrum enlargement is probably characteristic of coelurosaurs.
Improved posture and stability, however, is the purview of the hindbrain
(the cerebellum).

Interestingly, the authors note that "The cerebrum, cranial nerves,
olfactory bulbs, and optic lobes can all be reliably identified from
endocasts."  This may not be a general rule, because I recall Chris Brochu
pointing out that optic lobes did *not* leave an impression on theropod
braincases:

http://www.cmnh.org/fun/dinosaur-archive/2002Feb/msg00322.html

>      A parachuting origin of flight might create
> strong selection pressures in favor of barbs and
> barbules to help lock the feather together to resist
> the air currents as the animal fell. I wonder how
> breaking feather symmetry would effect a parachuting theropod....

A stiff central rachis would also also assist the feather in resisting
torsional forces during aerial descents.


David Marjanovic wrote:

> Hm. It is easy to imagine parachuting evolving from pouncing, but I 
> can't imagine the flight stroke evolving that way. 

Perhaps via the execution of the predatory stroke during these descents.



References:

Larsson, H.C. et al. (2000).  Forebrain enlargement among nonavian theropod
dinosaurs.  J. Vert. Paleont. 20: 615-618.