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Dino sex

A recent posting (not in any way a "discussion") made reference to
dinosaur pornography. This has brought up an issue I have always felt
has been neglected: dinosaur mating.

Dinosaur cloacas are often mentioned, but is there any actual evidence
that dinosaurs had a bird-like cloaca? If I remember correctly birds
do not have a penis-like structure but instead rely on a "cloacal
kiss". Crocodiles do have a penis (just one, not two as in many
lizards), although I think turtles have a more bird-like structure,
so clearly the bird-like cloaca is not universal to archosaurs.

A lot of attention is given to dinosaur feeding, defence, locomotion,
social interaction and brooding, but not to the act of mating itself.
The tripodal stance in some sauropods could have as much to do with
adopting a mating stance as it did for feeding purposes, and those
thumbclaws may have provided "grip" as well as (or instead of) being
purely defensive. Being able to "squat" backwards and take some of the
weight on the tail may have allowed sauropods to lay eggs without the
need to let them drop from a great height (although giraffe babies
drop seven feet to the ground and they seem to do okay). One alternative
to the "sauropod squat" would be to have rubbery egg shells (the
sea turtle approach), although clearly those eggs that have been
interpreted as being sauropod were hard shelled, which may rule this
line of inquiry out.

I remember one of the initial theories on the usefulness of tyrannosaur
forelimbs had to do with grasping the female during mating, so the
subject has not been entirely ignored. As to the actual mating postures
taken, dromaeosaurs with their ability to raise their tails by up to
90 degrees could easily have adopted a bird-like mating stance,
although such a posture would be clearly impossible with sauropods.
And what of those thyreophorans that had spikes around their flanks?
The twisted contortion act of modern lizards would have been difficult

All conjecture of course, with more questions than answers, but then
that seems to characterise much of palaeontology. Does anyone else
have any ideas on the subject? Any scientific discussion, however
conjectural, must be better than the recent "what's on your monitor"
discussion or the endo-ecto-mesothermy tally.

        Dann Pigdon
        Melbourne, Australia