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



>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 difference is that dogs and cats are capable of breaking through the 
eggshell and are able to feed on the newly-hatched young; the mammals that 
lived at the end of the Mesozoic were not equipped to do so.  The major groups 
of mammals that were around then were mouse-sized Insectivores (basically a 
generic placental), Early Marsupials, and Multituberculates (analogous to 
rodents).  None of these groups had the teeth or jaw strength to threaten 
dinosaur hatchlings.

The tortises evolved to their present status in isolation from the mainland and 
from predators.  As such, they have no defence against the modern mammalian 
predators.  Usually, introduced species will end up having a field day, so it 
is no suprise that the tortises are being nailed.

We have to be careful in projecting modern ecological scenarios into the fossil 
record; we need to know if we are comparing similar situations.  Basically, 
comparing an island scenario to a continental scenario is going to be a stretch.

Shalom,

Rob Meyerson

***
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