RE: mosasaur babies/no marine dinos

["Steve Brusatte" <dinoland@lycos.com>]

On Wed, 02 Jan 2002 05:42:03  
 Ken Kinman wrote:
>
>      It seems to me that dinosaurs simply never had the chance to evolve 
>into that niche because of competitive exclusion from other marine reptiles 
>that got there first.   This probably kept mammals from radiating into 
>marine niches as well (until the K-T extinction opened them up).
>      In others words, maybe it was more a matter of bad timing, rather than 
>something intrinsically preventing dinosaurs from evolving viviparous 
>survival mechanisms for permanent life in the open ocean (which has not been 
>a common occurence among amniotes, and therefore obviously not an easy thing 
>to do even without the pressures of competitive exclusion).
>     Birds and turtles may have been too specialized to evolve marine 
>vivipary, but some early dinosaurs may have had the potential to develop it 
>if only other marine reptiles hadn't beat them to it.

Bingo.  That's exactly what I think.  It's like asking: why are there no large 
bodied mammals during the Mesozoic?  Obviously no intrinsic features were 
preventing mammals from attaining large size during the Mesozoic.  The reason 
larger mammals appeared much later is because the large-bodied niches that were 
once held by dinosaurs were vacated by the K-T event.  I bet the same 
hypothesis can be used to explain why no marine dinosaurs have been found, 
although it is difficult to prove.  Of course, that is not to say that a marine 
dinosaur will never be found.  Perhaps there was a vacated niche somewhere 
during the Mesozoic that a marine dinosaur filled.  We may just find one 
someday.  

Steve

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