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Re: (fwd) Mammals as a cause of Dinosaur extinction



Garrison Hilliard wrote:

> Why does Stephen Jay Gould completely ignore the possibility that
> mammals
> may have been a factor in the extinction of the dinosaurs some 65 mya.
> Instead, he says that mammals and dinosaurs co-existed throughout the
> Jurassic and Cretaceous and that this demonstrates that mammals did
> not
> consume the Dinosaur young leading to the demise of that group. I
> remember
> this theory from a 1950's textbook.

In 1950, it was thought that mammals were a new group, recently evolved
in the Late Cretaceous.  We now know that mammals were around all
through the Jurassic and Cretaceous.

> 
> Giant reptiles (turtles) have "ruled" the Galapagos islands for a long
> time. It is my understanding that recently imported dogs and cats have
> caused a decline in the turtle population due to their predation of
> turtle
> hatchlings. The same predation has also reduced the population of the
> other
> Galapagos "rulers", the Iguanas. Why is it not a feasible possibility
> that
> newly evolved (Late Cretaceous that is) placental mammals damaged the
> dinosaur population by eating their young. The adult Dinosaurs (just
> like
> adult Galapagos turtles) would be invulnerable to mammal attack but
> their
> young would not be so lucky. Question--- When did definable placental
> mammals evolve? Was it not in the Late Cretaceous, at about the same
> time
> that the number of Dinosaur species declined?

Placentals did evolve in the Late Cretaceous -- there are a few in the
Flaming Cliffs and Ulaan Bataar beds.  However, they were little
different from their older relatives in the ecological niches they
occupied.  There's no reason to think that placentals would have had any
more effect on dinosaur nests than their nonplacental ancestors did.

As for Galapagos tortoises, consider the fact that these animals have
evolved in isolation not only from egg-eaters but from all predators of
any kind for several million years, which dinosaurs did not do.  Mammals
were an ever-present factor in the world of the dinosaurs.

-- JSW