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Re: No Cretaceous placental mammals?
<<ancestors of modern placental mammals were very small, and on total
conjecture probably hatched their eggs internally like some sharks do now.>>
I'd imagine, the most recent common ancestor of myself and a marsupial was
probably using a marsupial-like reproduction system, Rob; relatively
early-born, poorly-developed deliveries. The oldest known eutherian (=
Placentalia plus more intimate relatives) is 125 million year old /Eomaia/
from Liaoning. The pelvis has a rather narrow construction, and it's been
said that this wouldn't have allowed for the arrival of well-developed kids.
The Mesozoic - more than just the dinosaur