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RE: Vestigial Arms (was: Theropod limbs - how mobile?)

David Marjanovic wrote:

> I'm thinking about whether this would imply sexual dimorphism (probably
>  not testable because of the sample size)... and whether it's possible 
> to hold a tyrannosaur with such hands without inflicting serious wounds 
> to it. :-/

I think it was Osborn who first suggested that male tyrannosaurids used
their forelimbs as claspers during copulation.

For boid snakes, both males and females have pelvic spurs - but only the
males use them for copulation.  However, males tend to have proportionally
larger pelvic spurs than females - at least for _Python reticulatus_ (Shine
et al., 1998; J. Zool. Lond. 244: 405-414).

The pelvic claspers of elasmobranchs (sharks, rays) are found only in males,
and serve as an intromittent organ (transfer of sperm to the female).  The
extinct placoderms also had them.



Timothy J. Williams, Ph.D. 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233