© 2006 The McGraw-Hill Companies, Inc. All Rights reserved. Chapter Twelve The Early Primate Fossil Record and the Origins of the Hominins

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

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

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

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

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

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

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

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

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

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

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

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