Therapsid

Therapsid, any member of a large group of reptiles from which mammals eventually evolved. Therapsids flourished during the Late Paleozoic and Early Mesozoic eras, from about 250 million to about 190 million years ago, and subsequently became extinct. Therapsids were four-legged terrestrial reptiles. Some were vegetarian, others were carnivorous. Some therapsids were the size of small rodents, others larger than a modern hippopotamus. Therapsids had certain attributes typical of mammals; for example, the teeth of some species had differentiated into cutting incisors, tearing canines, and grinding molars.

Scientific classification: Therapsids made up the order Therapsida.