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MAMMALIA PREHISTORIA The evolution of mammals has passed through many stages
since their first appearance in the late Carboniferous period. By the
mid-Triassic, there were many species that looked like mammals. The lineage leading
to today's mammals split up in the Jurassic. Later on, the eutherian and
metatherian lineages separated; the metatherians are the animals more closely
related to the marsupials, while the eutherians are those more closely
related to the placentals. Since Juramaia, the earliest known eutherian,
lived 160 million years ago in the Jurassic, this divergence must have
occurred in the same period. After the Cretaceous–Paleogene extinction event
wiped out the non-avian dinosaurs (birds are generally regarded as the
surviving dinosaurs) and several other mammalian groups. |
