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Placentals are better adapted to terrestrial life than marsupials and monotremes because they show a greater diversity of locomotory types. Discuss.
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Placentals are better adapted to terrestrial life than marsupials and monotremes because they show a greater diversity of locomotory types. Discuss. Introduction: The evolution of mammals. Mammals probably first evolved in the Triassic period 245 Million Years (m.y.) ago. Of these first mammals no living examples have survived into the modern era. All three mammal groups existing today are derived from a group that evolved some 230 m.y. ago called the holotheres, because of the arrangement of their teeth. Of these the oldest are the Prototheria, or monotremes which survive as six species in Australia and New Guinea in two groups, the duck-billed platypus and the echidnas. Prototheria lay eggs that are incubated and hatched outside the reproductive tract of the females. Nevertheless they are endothermic, hairy, milk-producing vertebrates with reduced teeth, thus qualifying as vertebrates. The remaining two groups belong to the subclass Theria. They are viviparous (give birth to...
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