© 2006 the mcgraw-hill companies, inc. all rights reserved. chapter twelve the early primate fossil...

© 2006 The McGraw-Hill Companies, Inc. All Rights reserved.

Chapter Twelve

The Early Primate Fossil Record and the Origins of the Hominins

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Evolution of the Early Primates

• The earliest mammals evolved during the Mesozoic era.

• By Paleocene times, at the beginning of the Cenozoic era, all of the dinosaurs and many other forms of life were extinct and mammals began their adaptive radiation.

• By the start of the Eocene, most of the modern orders of mammals had appeared.

• At the end of the Mesozoic, great forests evolved with flowering trees that provided protection and food for early primates.

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The Plesiadapiformes

• The earliest primates may be the Plesiadapiformes, who were small, arboreal quadrupeds.

• The Plesiadapiformes had a long snout, small brain, and claws, and lack both a postorbital bar and a grasping big toe. – Because of this, many primatologists believe the

plesiadapiformes were not direct ancestors of later primates.

• Two genera of plesiadapiformes are Purgatorius and Plesiadapis.

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The Early True Primates and the Origins of the Lemuriformes and Tarsiiformes

• Two distinct groups of primates appeared at the beginning of the Eocene in both Europe and North America: – the Adapidae – Omomyidae

• The members of the Adapidae resemble in many ways the modern lemurs and lorises and the Omoyidae resemble the living tarsiers.

• The earliest loris-like and galago-like primates were discovered in Egypt and date from the Middle Eocene. – The earliest lemur is from the Early Oligocene of Pakistan. – Middle and Late Eocene fossils from Egypt and China represent

the earliest tarsiers.

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Evolution of the Anthropoidea

• The suborder Anthropoidea includes the living monkeys, apes and humans.

• The earliest anthropoids in the fossil record date from the Middle Eocene and are known from sites in Africa and Asia.

• It is widely believed that Africa is the most likely center for early Anthropoid evolution that took place in the Late Eocene.

• The Anthropoids most likely did not reach Asia until the Late Oligocene

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The Anthropoids of the Fayum

• The Fayum of Egypt dates from the Late Eocene and Early Oligocene.

• The primates of the upper levels belong to the families Parapithecidae and Propliopithecidae.

• The Parapithecidae, including Aegyptopithecus, may represent a group of primates ancestral to both the cercopithecoids and the hominoids.

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The Evolution of the New World Monkeys

• The New World monkeys, the ceboids, are probably derived from early African anthropoids that traveled across the then-narrower Atlantic Ocean on natural rafts.

• The earliest-known ceboid, Branisella, dates from the Late Oligocene of Bolivia.

• The evolution of the ceboids into their present subfamilies took place by the Middle Miocene.

• Although New World monkeys and Old World monkeys evolved independently, there are many similarities in their appearance due to parallelism.

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The Evolution of the Old World Monkeys

• The Old World monkeys, the cercopithecoids, were relatively scarce in the Miocene.

• By the Pliocene and Pleistocene, they became common animals, especially in Africa.

• The earliest-known fossils of Old World monkeys belong to the genera Prohylobates and Victoriapithecus and make up the family Victoriapithecidae.

• Beginning in the Late Miocene, the monkeys underwent a divergence into two subfamilies, the Cercopithecinae and the Colobinae.

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Evolution of the Hominoidea

• Fossil hominoids are well-known from the Miocene, during which time they underwent a major adaptive radiation.

• The earliest hominoids to appear in the fossil record date between 22 and 18 million B.P. from early Miocene fossil beds of east Africa and Saudi Arabia. – They most likely evolved from Oligocene primates, such as the

propliopithecids.

• Most of the Miocene hominoids disappeared by around 8 million years ago, during the Late Miocene. – One genus, Gigantopithecus, survived long enough to be

contemporary with members of the genus Homo.

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Hominoids of the Early Miocene

• The fossil hominoids of the Early Miocene radiation belong to a number of genera.

• They tend to fall into two major groups, represented by the genera Proconsul and Afropithecus.

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The Miocene Hominoid Radiation

• By the end of the Early Miocene, most of the African hominoids were extinct.

• But migration from Africa into Europe and Asia was now possible and at least one lineage survived and moved into Eurasia.

• In Eurasia, the hominoids underwent an extraordinary diversification and adaptive radiation.

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Miocene Hominoids

• The hominoids of the Middle and Late Miocene can be divided into two general groups: – Those with thick enamel on their molars (associated with drier

habitats)– Those with thin enamel on their molars (associated with wetter

habitats).

• The hominoids of the Miocene include the genera Dryopithecus, Pliopitthecus, Sivapithecus, Oreopithecus, and Gigantopithecus.

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The Origins of the Hominins

• The origins of the hominins lie in the diverse group of hominoids found in the Miocene, although links with known fossil species are problematic.

• Several new species have been found recently that fill in a gap in the fossil record from about 8 to 4 million years ago.

• These species include Sahelanthropus tchadensis, Orrorin tugenensis, Ardiptihecus kadabba, and Ardipithecus ramidus.

© 2006 the mcgraw-hill companies, inc. all rights reserved. chapter twelve the early primate fossil...

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