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.
Rieppel and deBraga conducted a detailed computer analysis of reptiles which revealed that turtles share more characteristics with diapsids -- modern-day reptiles -- than with anapsids, the more primitive reptile clade to which they long have been assigned.
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.