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The evolutionary split between placentals and marsupials occurred 125-160 million years ago, in the Middle Jurassic-Early Cretaceous period. Presently, close to 70% of the 334 extant marsupial species are concentrated on the Australian continent, including mainland Australia, Tasmania, New Guinea, and nearby islands.
Other similar basal primates were widespread in Eurasia and Africa during the tropical conditions of the Paleocene and Eocene. Purgatorius is the genus of the four extinct species believed to be the earliest example of a primate or a proto-primate, a primatomorph precursor to the Plesiadapiformes, dating to as old as 66 million years ago.
The situation in West Africa is difficult to interpret due to a sparsity of fossil evidence. Homo sapiens seems to have reached the western Sahelian zone by 130,000 years ago, while tropical West African sites associated with H. sapiens are known only from after 130,000 years ago.
Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
Fossils found at Lightning Ridge, New South Wales, suggest that 110 million years ago Australia supported a number of different monotremes, but did not support any marsupials. [4] Marsupials appear to have evolved during the Cretaceous in the contemporary northern hemisphere, to judge from a 100-million-year-old marsupial fossil, Kokopellia ...
Primates first evolved sometime between the Middle Cretaceous and the early Paleocene periods on either the supercontinent of Laurasia or in Africa. [2] According to molecular clock studies, the last common ancestor of all primates dates to around 79.6 mya, [ 3 ] although the earliest known fossil primates are only 54–55 million years old. [ 4 ]
Opossums (/ ə ˈ p ɒ s ə m z /) are members of the marsupial order Didelphimorphia (/ d aɪ ˌ d ɛ l f ɪ ˈ m ɔːr f i ə /) endemic to the Americas.The largest order of marsupials in the Western Hemisphere, it comprises 126 species in 18 genera.
The southern route dispersal is primarily linked to the Initial Upper Paleolithic expansion of modern humans and "ascribed to a population movement with uniform genetic features and material culture" (Ancient East Eurasians), which was the major source for the peopling of the Asia–Pacific region.