re:copulation

[ornstn@hookup.net (Ronald Orenstein)]

>It is possible that dinosaurs had a penis of similar construction to
>extant primitive birds like the ostrich.  In dinosaurs size might have
>been important in avoiding damage to the female.  Obviously this was not
>always successful.  I have not looked at ostriches penes closely,
>perhaps someone can tell us if they were able to do the 'helicopter
>twist', or whether they are of similar construction to mammal penes.

Strictly speaking birds do not have a penis, but penis-like organs are found 
in tinamous, ratites, cracids and waterfowl.  According to Lofts and Murton, 
"Reproduction in birds" (Chapter 1 in Avian Biology vol. 3, Academic Press 
1973), "In waterfowl the penis is a vascularized sac which can be protruded 
by a muscle and retracted by a ligament.  The ligament is bound spirally 
round the sac and gives the penis a twisted appearance.  Sperm move along a 
spiral groove that passes from the cloacal papillae at the organ's base to 
its tip.  Hohn (1960) has shown that the weight of the penis in the Mallard 
(Anas platyrhynchos) increases sixfold with the onset of the breeding 
season... Females of those species in which the male possesses a "penis" 
have a homologous but reduced structure termed the "clitoris".  Their 
cloacal opening is slightly modified to receive the intromissive organ of 
the male."

The authors go on to suggest that the evolution of such structures in 
different groups of birds may be linked to polygamous or polyandrous 
breeding systems, in which the time of contact between thesexes may be short 
and there may be an advabtage in developing a highly efficient copulation 
mechanism.

What this has to do with dinosaurs I'm not sure, except that if there is 
variability in birds on this point I suspect there may well have been even 
greater variability among dinosaurs which are a larger taxonomic subset.  Is 
there any hard evidence (if you'll pardon the expression) that any dinosaur 
had an intromittent organ?
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
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