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RE: Continental predators, etc.



> > Ichtyosaurs definitely were
> > viviparous and many extant snakes are ovoviviparous (the eggs hatch as
> > they are laid). Admittedly no birds have ever been viviparous as far as
> > known (though it has been suggested that Hesperornis 
> > may have been). 

A couple quick points regarding evolution of reproductive 
modes that may be counter-intuitive in some ways:  In 
snakes, and some other reptile species, ovoviviparous 
species have arisen in multiple lineages.  There does not 
seem to be differential survival between closely related 
oviparous and ovoviviparous species that live in the same 
environments.  Furthermore, there is at least one example 
(Calabar "Pythons") that have reverted to an oviparous 
reproductive mode, despite plenty of nest raiding species 
in their environment.  To state that viviparous modes are 
selected for in high-predation environments (and that 
oviparous modes are selected against) may therefore be far 
too simplistic, including situations involving dinosaur 
taxa.

Michael Habib
mbh3q@virginia.edu