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Reptile-Bird-Dinosaur-Penis Connection



  We're discussing reproduction in my biology class
and I started wondering about a way to figure out the
connection between birds, dinosaurs, and "regular"
reptiles . . .

  Most male reptiles have some sort of penis-like
structure(s) for internal fertilization.  Male birds
lack such an organ and only use a cloaca kiss.  But
birds are "more advanced" than reptiles.  I put that
in quotes because if this feature is any sort of
indication, it might suggest that birds diverged off
the reptilian tree before a penis structure is evolved
by the main reptilian group.  Tuataras, primitive
reptiles, do not have such a structure as well, so
maybe birds split off around the same time.

  This might help us sort out dinosaurs as well.  Does
that specimen of Scipionyx show any sort of sex
organs?  If any similarly preserved fossils can be
found (and if this guesswork is logical!), then may
the presence of a penis can tell us something.  If
dinosaurs have one (or two, like snakes/lizards),
maybe they diverged later in time, after the penis was
evolved.  If not, perhaps they diverged earlier at a
time close to the bird split-off, if indeed birds were
an early offshoot of the reptile group.

  When I brought this up in class, my teacher raised
the devil's advocate, saying that birds could may have
lost the penis due to flight adaptations, as in bats
or whales for hydrodynamics.  But that's an incorrect
analogy, as those animals retain a penis and merely
keep it internally.  Which backs up this hypothesis,
for if birds ever had a penis, it would be retained. 
I don't know, can a structure like that really become
vestigial over time, like legs?

  I'm only in a high school biology AP class, so my
reasoning and information may not be all correct.  So
I'm posting these hypothesis on the List -- would the
experts take a look and see if my thinking makes any
sense?  Thank you.


Ben Landis
diverben@yahoo.com
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