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Re: Dinosaur "baculae"

At 10:20 AM 9/8/95, Ronald Orenstein wrote:
>    >   I've devoted a little thought to the process, especially having
>>seen some peculiar bones associated with the occasional sauropod skeleton
>>that don't resemble anything else in the skeleton, except possibly a vastly
>>deformed rib -- a sauropod baculum?
>I should be extremely surprised to learn that any dinosaur had a baculum, as
>this is a feature of the mammalian penis which (by virtue of its being
>divorced from the digestive system except in Monotremata which I think lack
>baculae) is not exactly homologous to the intromittent organ of any
>non-mammalian vertebrate.

        It's quite possible that the os baculum is derived from the
epipubis (although this is only a hunch).  The os baculum is only found in
therian mammals, all of which have lost the epipubis.  Conversly,
monotremes and marsupials don't possess baculae, but retain the epipubis.
As for dinosaurs, its pretty unlikely that they possessed either a baculum
or a true penis, as neither crocodylians or birds possess either.  In
addition, The largest crocodiles surpassed many dinosaurs in size, and
(currently) nobody is hypothesizing unique reproductive morphology for
them.  Male dinosaurs were big, but so were the females.  Why would their
size also necessitate specialized genitalia?

Jason J. Head
V.P. graduate student
Dept. of Geological Sciences
Southern Methodist University
Dallas, Tx. 75275