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CENOZOIC ERA

PALEOGENE PERIOD

Paleocene Epoch

65-55 million years ago

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prosimian

Placental mammals began to diversify into modern groups either just before or just after Mesozoic Era ended. Rodents and primates share a more recent common ancestor. After the divergence of the rodent and rabbit lineages, tree shrews and flying lemurs formed the sister groups of primates.

Placental mammals have been classified into four superorders, two of which (Xenartha and Afrotheria) are considered to be more primitive. The superorder Xenarthra originated in South America and includes armadillos, anteaters, and sloths. The superorder Afrotheria originated in Africa and includes elephants, sea cows, extinct demostylans, hyraxes, aardvarks, elephant shrews, and tenrecs (although some feel that golden moles and tenrecs should be classified in their own group). The superorder Euarchontoglires includes the Glires (rodents and rabbits) and Euarchonta (tree shrews, flying lemurs, and primates). The last of the superorders to evolve is the group Laurasiatheria, which includes whales artiodactyls, perrisodactyls, carnivores, and bats (Carter, 2004).