- Any of various amniotes with one temporal opening on each side of the skull. Synapsids emerged in the late Permian Period and were characterized by carrying their limbs under their body and developing front teeth that were different from their back teeth. One group of synapsids, the therapsids, gave rise to the mammals. Compare anapsid diapsid therapsid.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Examples from the Web for synapsid
A few years ago a Permian bed in Russia yielded a most interesting series of remains of Synapsid reptiles.
Their remains fall into two great groups, which are known as the Diapsid and the Synapsid reptiles.