Primates
In early classification schemes the primate order had two suborders: prosimians (‘before apes’), which included lemurs, lorises and tarsiers; and anthropoids (‘man-like’), which included the monkeys and apes. When the tarsiers were shown to be more closely related to the simians they were transferred to the anthropoids, which were renamed ‘dry nosed’ haplorrhines (‘simple noses’), and prosimians were renamed ‘wet-nosed’ strepsirrhines (‘bent-noses’).
During the Palaeocene, forests were occupied by multituberculates and the primate-like plesiadapids. The multituberculates were crowded out by rodents, and the plesiadapids were displaced by rodents and two groups of primates: the adapids (Cuvier thought that adapis – towards the sacred bull Apis – might have been related to the artiodactyls), and the omomyids (‘shoulder mice’). The adapids are considered as members of the strepsirrhines, and the omomyids are considered as members of the haplorrhines. Omomyids perished about 30 mya and the adapids survived until about 10 mya.
Haplorrhines have two infraorders: tarsiiformes and simiiformes. The simiiformes are arranged in two groups named platyrrhines (‘flat-noses’) or New World monkeys of South and Central America, and catarrhines (‘hanging noses’) or Old World monkeys of Africa and Southeast Asia.
The platyrrhines are conjectured to have migrated across the Atlantic to South America on a raft of vegetation. The split between Old and New World primates apparently took place about 40 mya when the distance between Africa and South America became too great to traverse. About 25 mya the catarrhines split into the Old World monkeys and the apes. This divergence was predated by an early catarrhine Aegyptopithecus (‘Egyptian ape’) at 35 mya. It had many primitive characters but its advanced features were more like those of apes than monkeys and it could be a link to the higher primates.
The apes (chimpanzees, gibbons, gorillas, orangutans and humans and related forms) are classified as the superfamily Hominoidae (‘manlike’). Gibbons and orangutans live in Southeast Asia; gorillas and chimpanzees are found in Africa.
The gibbons (the ‘lesser apes’) branched off 18 mya into the family Hylobatidae (‘tree walkers’), and the ‘great apes’ (orangutans, gorillas, chimpanzees and humans) became the family Hominidae. The orangutans branched off 14 mya into the subfamily Ponginae (Pongo), and the African apes and humans became the subfamily Homininae. The gorillas branched off 7 mya into the subfamily Gorillinae, and the chimpanzees and humans became the tribe Hominini. The chimpanzees branched off 4-6 mya into the tribe Panini, and 2.3 mya humans became the subtribe Hominina.
Hominoids (apes)
The earliest remains of Proconsul (the name was a humorous reference to a performing chimpanzee named Consul), dated at 25-23 mya, come from Africa. There were several species, including one as small as a gibbon and another that was the size of a female gorilla. One of the smaller specimens had a reasonably large brain (about 167 cc) and weighed about 9 kg (20 lb), i.e. its brain was large relative to its body, compared to living monkeys. Afropithecus (‘African ape’), dated at about 18 mya, and Kenyapithecus, dated at 14 mya, are progressions towards later hominoids. Dryopithecus (‘woodland ape’) dated at 12 mya has been subject to many different interpretations since its discovery.
Hominids (great apes)
The earliest known hominoid outside of Africa is Sivapithecus (Siva + ‘ape’), dated at 12.5-10.5 mya. Similarities in the structure of face and palate suggest that Sivapithecus is ancestral to the orangutans. Ramapithecus (‘Rama + ape’), dated at about 13 mya, once thought to be ancestral to humans, is now known to be closer to Sivapithecus. The huge ape Gigantopithecus (‘giant ape’), dated at 9.0-0.1 mya, is thought to be in the line that led to the orangutans.
Hominines (African Apes)
The oldest known hominine fossils are Sahelanthropus tchadensis (‘Sahel man from Chad’), with a cranium named Tomai (‘hope of life’), dated at 7 mya; Orrorin tugenensis (‘original man from Tugen’) dated at 6.1 mya; and Ardipithecus ramidus (‘ground man-root’) dated at 4.4 mya.
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