Cecil,
How about letting us know what the exceptions to the belly button rule are. Do platypuses have belly buttons? Echidnas?
Seeing as how they lay eggs, I rather think not.
Neither monotremes (whom some classifiers now exclude from Mammalia to begin with) nor marsupials have umbilical cords; consequently, they do not have navels. In theory, no placental mammal should lack a navel, though I suppose it is possible that there may be some species in which it is (or very nearly is) indetectable.
Amnionic?
What’s up with Unca Cecil? Isn’t that “amniotic”? I don’t blame him, but to find a typo in a SD answer is a cosmic success. Yes, I know Obama won, maybe that explains it.
While cats and dogs certainly do have an umbilical scar Cecil is correct in saying that they don’t have belly buttons per se. I think the reason for this is that the umbilicus is chewed/pulled off by the dam (anything that’s left shrivels up as its vasculature naturally closes).
I believe when human babies are born the umblicus is cut and tied; I’ve always assumed that this is why you get that little knotlike scar, rather than it being a human/primate specific thing. Anyone got any pictures of other primate navels (come on now, own up)?
At least included the obvious exceptions of Adam and Eve.
I’m guessing that means that the first cats didn’t have belly buttons either.