http://en.wikipedia.org/wiki/Mammal
One synapsid group, the pelycosaurs, included the largest and fiercest animals of the early Permian.
Therapsids descended from pelycosaurs in the Middle Permian, about 265 million years ago, and took over their position as the dominant land vertebrates.They differ from pelycosaurs in several features of the skull and jaws, including: largertemporal fenestrae and incisors which are equal in size.The therapsid lineage leading to mammals went through a series of stages, beginning with animals that were very like their pelycosaur ancestors and ending with probainognathian cynodonts, some of which could easily be mistaken for mammals.
One synapsid group, the pelycosaurs, included the largest and fiercest animals of the early Permian.
Therapsids descended from pelycosaurs in the Middle Permian, about 265 million years ago, and took over their position as the dominant land vertebrates.They differ from pelycosaurs in several features of the skull and jaws, including: largertemporal fenestrae and incisors which are equal in size.The therapsid lineage leading to mammals went through a series of stages, beginning with animals that were very like their pelycosaur ancestors and ending with probainognathian cynodonts, some of which could easily be mistaken for mammals.
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