; subphylum Vertebrata, class Reptilia)
A subclass of reptiles which includes the Pelycosauria and Therapsida. The pelycosaurs appeared in the upper Carboniferous and disappeared in Early Permian times, displaced by the therapsids to which they had given rise. The therapsids flourished in the latter part of the Permian and in the Triassic, but dwindled to extinction in the Early Jurassic. The therapsids are the ancestors of the mammals, and share in common with them a synapsid skull (i.e. a skull with one temporal opening above which the postorbital and squamosal bones meet). See also Ichthyopterygia.
Subjects: Zoology and Animal Sciences — Earth Sciences and Geography.