| Noun | 1. | Synapsida - extinct reptiles of the Permian to Jurassic considered ancestral to mammals class Reptilia, Reptilia - class of cold-blooded air-breathing vertebrates with completely ossified skeleton and a body usually covered with scales or horny plates; once the dominant land animals order Therapsida, Therapsida - extinct mammal-like reptiles found inhabiting all continents from the mid Permian to late Triassic Ictodosauria, order Ictodosauria - extinct reptiles of the later Triassic period order Pelycosauria, Pelycosauria - edaphosaurus; dimetrodon class - (biology) a taxonomic group containing one or more orders |