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Re: Differences between *Vancleavea* and thalattosaurs



David Peters <davidpeters@att.net> wrote:


> Then remember, "the apple doesn't usually
> fall far from the tree" which is another way of saying
> evolution works in small incremental steps. 


This is not always true.  Developmental studies have taught us that certain 
major changes can be sudden, rather than representing a culmination of "small 
steps".  Major morphological transformations can be determined by one or a few 
key developmental genetic changes.  

In other words, certain changes in evolution are likely to have occurred 
rapidly, with few or no intermediate stages.  For example, the addition of an 
extra vertebra into the neck, or the switch from procoely to opisthocoely (both 
seen in sauropod evolution) probably occurred in a single step.  

The extreme elongation of the fingers of bats could have occurred by relatively 
minor changes to a single developmental pathway (see work of Karen Sears &c).  
The same might be true of pterosaurs.  

Arthropods could gain or lose segments in a single step - with the process 
governed by essentially the same mechanism by which sauropods gain or lose 
cervical vertebrae.  

All sorts of evolutionary jumps no doubt went on in the evolution of feathers. 

And so on...


Cheers

Tim