anapsid

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Related to Anapsids: diapsid

anapsid

a member of the Anapsida, a group of reptiles in which the skull lacks a temporal FOSSA. The Anapsida include Seymouria, tortoises and turtles.
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All reptiles living today are diapsid, with the exception of turtles, previously thought to be anapsid, making them the only living primitive reptiles.
When all of the data -- much of it provided by deBraga, whose research focuses on Paleozoic reptiles -- was crunched through the computer, "we found that turtles flipped from anapsid to diapsid," Rieppel explains.
According to the standard evolutionary story, turtles retain some characteristics of the ancient anapsids. As such, biologists have regarded them as an example of the stock from which reptiles, birds, and mammals later evolved.