Stasis

A fossil that once lined a mule track in Iraq has revealed the surprising survival of a group of ichthyosaurs, marine reptiles that swam the seas more than 66 million years ago. 

Researchers had previously believed that ichthyosaurs declined throughout the Jurassic Period, which lasted from 199 million to 145 million years ago, with the only survivors rapidly evolving to keep ahead of repeated extinction events. The new fossil, however, dates from the Cretaceous Period, which lasted from 145 million to 66 million years ago. It looks remarkably like its Jurassic brethren, revealing a surprising evolutionary [stasis].

http://science.nbcnews.com/_news/2013/05/15/18280065-fossil-reveals-surprising-survival-of-marine-reptile?lite