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Re: Endotherms and reproduction

Martin Human wrote:

> So, (tongue firmly in cheek) can anyone say a) why the need in mammals
> vs. any other endothermic creature, or b) can we deduce birds are
> actually ectothermic or c) did dinos sport a scrotum?
> cheers, martin

Just to make it clear at the outset, I don't really have any of the
answers. Engage speculation drive, warp factor eight...

I suspect (and it's no real big gamble) that archosaur and mammalian
physiology is quite different. Mammalian testes are at their most
fertile when a few degrees cooler than the body, and should they get too
warm (such as failing to drop from the body cavity) it can lead to
testicular cancer. Mammals being an inventive bunch (they built the
computer I'm using now), the scrotum has been exapted by marsupials to
form a pouch in the females (since they have little use for a scrotum).
Because of this, marsupial male genitals are now "upside down", with the
scrotum above the penis. Hence kangaroos have an almost prehensile
appendage that has to bend around 90 degrees. But that's really neither
here nor there, just (hopefully) of trivial interest.

That said, some species of mammals seem to have internal testes (the
cetaceans for example). Perhaps early on in archosaur evolution there
was a need to have them internally, to reduce the bulk or perhaps the
aero/aquadynamic characteristics of the body. I'm also assuming that
mammalian and archosaur endothermy is achieved by different chemical
means? Perhaps the mammalian endothermic condition resulted in the need
for external gonads, a need that was never present in any other
endothermic lines of evolution.

All the same, could you imagine the sheer dumb-founding awe of a
sauropod scrotum? 


Dann Pigdon                   Australian Dinosaurs:
GIS Archaeologist           http://dannsdinosaurs.terrashare.com
Melbourne, Australia        http://home.alphalink.com.au/~dannj/