Though their first members appeared in the Mesozoic, it was not until the Cenozoic that most of their modern orders started to evolve.
Much evolutionary study of this group focuses on their distinctive middle ear bones. Therapsids are early ancestors of these, and include cynodonts, which give rise to these in the late Triassic. Though their first members appeared in the Mesozoic, it was not until the Cenozoic that most of their modern orders started to evolve. The two major types are australosphenids, which include placentals, and theria, which include monotremes, which unlike most of these animals lay egg. Named for nursing their young with milk, for 10 points, name this class of vertebrate animals which includes dogs, bats, and humans.
Much evolutionary study of this group focuses on their distinctive middle ear bones.
{Mammals} [accept {mammalia}]