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MESOZOIC ERA

TRIASSIC PERIOD

251-201 million years ago

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CYNODONT

Advanced cynodonts evolved even more mammalian modifications of the skull.


Although the frontal bone changed little from the cynodonts to the first mammals, three ancestral bones around the orbit were--the prefrontal, postfrontal, and postorbital. In later cynodonts, the prefrontal and postorbital bones were lost, and thus the postorbital bar which separated the orbit and jaw musculature was lost. The alisphenoid moved closer to the basisphenoid. Advanced cynodonts evolved tooth occlusion so that food could be ground between matching surfaces of upper and lower teeth. They also developed multirooted postcanine teeth.