  therapsida is a group of synapsids, and includes mammals and their ancestors.therapsid (fossil reptile order) - encyclopedia britannica many of the traits today seen as unique to mammals had their origin within early therapsids, including having their four limbs extend vertically beneath the body, as opposed to the sprawling posture of other reptiles. the earliest fossil attributed to therapsida is tetraceratops insignis from the lower permian.m. laurin & r. r. reisz. 1996. the osteology and relationships of tetraceratops insignis, the oldest known therapsid. journal of vertebrate paleontology 16(1): 95-102.j. liu, b. rubidge & j. li, new basal synapsid supports laurasian origin for therapsids, 2009, acta palaeontol. pol., 54 (3): 393-400 therapsids evolved from pelycosaurs (specifically sphenacodonts) 275 million years ago. they replaced the pelycosaurs as the dominant large land animals in the middle permian and were replaced, in turn, by the archosauromorphs in the triassic, although one group of therapsids, the kannemeyeriiforms, remained diverse in the late triassic. the therapsids included the cynodonts, the group that gave rise to mammals in the late triassic around 225 million years ago. of the non-mammalian therapsids, only cynodonts and dicynodonts survived the triassicâjurassic extinction event. the last of the non-mammalian therapsids, the tritylodontid cynodonts, became extinct in the early cretaceous, approximately 100 million years ago. ==characteristics==  while the early therapsids had skulls very similar to those of their pelycosaurian ancestors, morphological difference is exhibited within the post-cranial morphology. ===legs and feet=== their legs are
Animal_orders Therapsids