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THE MAMMALS
~210 million yearsThe evolution of mammals within the synapsid lineage (mammal-like-reptiles) was a gradual process that took approximately 70 million years, beginning in the mid-Permian. By the mid-Triassic, there were many species that looked like mammals, and the first true mammals appeared in the early Jurassic . The earliest known marsupial, Sinodelphys, appeared 125 million years ago in the early Cretaceous, around the same time as Eomaia, the first known eutherian (member of placentals' "parent" group); and the earliest known monotreme, Teinolophos, appeared two million years later. After the Cretaceous-Tertiary extinction wiped out the non-avian dinosaurs (birds are generally regarded as the surviving dinosaurs) and several other mammalian groups, placental and marsupial mammals diversified into many new forms and ecological niches throughout the Tertiary, by the end of which all modern orders had appeared. (click to see all the article on Wikipedia)
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