ANT203 CHAPTER 9 - Introduction to Physical Anthropology

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Maryam Nargolwalla

CHAPTER 9: OVERVIEW OF THE FOSSIL PRIMATES I. Introduction a) This chapter traces primate evolution starting from the earliest fossil evidence of primate-like mammals of the Paleocene up through the hominoid radiation of the Miocene. i) Most of the fossil groups discussed in this chapter are not related to any of the living primates and only a few are related to our hominid ancestors. b) Background to primate evolution: Late Mesozoic i) Primate origins are not well understood. ii) The divergence of the order primates probably began during the Cretaceous period of the Mesozoic Era. (1) The living members of the order Primates are closely related to the extinct early primate-like mammals of the order Plesiadapiformes and to the extant members of the orders Scandentia and Dermoptera. (a) Most scientists place these four orders into the superorder Archonta. II. Primate Origins a) The conventional wisdom is that primate-like mammals first evolved in the early Paleocene. However, new molecular evidence suggests that the LCA between primates and their Archontan relatives was present during the Cretaceous period. (1) Combining molecular and morphological evidence yields a divergence time for the LCA of between 55.8 and 90 mya. III. Made to Order: Archaic Primates a) The plesiadapiforms underwent an adaptive radiation between 64 and 52 mya. i) Six families are known from this group, but two genera, Plesiadapis and Carpolestes are of particular interest to us. (1) Plesiadapis probably originated in North America and spread into Europe. (a) They have rodent-like dentition (but the incisors did not grow continuously) that indicates they had a diet rich in leaves supplemented by fruit. (2) Carpolestes has features of its postcranial anatomy that indicate adaptations to an arboreal environment. (a) A recently discovered skeleton indicates that Carpolestes possessed nails rather than claws. b) Out of order i) Although Plesiadapis and Carpolestes share some skeletal characteristics with true primates, cladistic analyses indicate that they should not be placed in the order Primates. IV. Eocene Euprimates a) Eocene euprimates (mammals with derived modern primate features) appear nearly simultaneously in North America, Asia, and Europe around 55.8 mya. i) However, a close examination of the fossil record indicates that Asia may have been the home of the euprimates. ii) The Eocene euprimates are generally divided into two superfamilies: the lemur-like Adapoidea and the tarsier- or galago-like Omomyoidea. (1) Both groups are well known from cranial, dental, and postcranial remains from North America, Europe, Asia, and Africa. b) Lemur-like adapoids are represented by more than 35 genera that are divided into 5 geographic families including the notharctids of (primarily) North America, the adapids of Europe, and the amphipithecids of Asia. i) Their dental formula is ii) Cantuis, the earliest notharctid, was probably a diurnal frugivore. iii) The adapids appeared in Europe near the end of the Eocene and quickly went extinct. iv) The amphipithecids posses anthropoid-like dental traits that are probably homoplasies. c) Evolution of true lemurs and lorises i) Ancient adapoids and modern lemurs resemble each other only because modern lemurs retain some ancestral traits. (1) Adapoids lack the dental specialization of the lemur’s dental comb. ii) It is possible that modern lemurs originated on the African mainland because the non-adapoid late Eocene specimen of the genus Wadilemur from Egypt may have possessed a dental comb. (1) There are numerous large-bodied subfossil lemurs on Madagascar, but few true fossils of lemurs are found there. d) Tarsier-like omomyids i) The omomyids are typically divided into three families: one from North America, another from Europe, and the third from Asia. ii) European members of this group resemble living tarsiers in a number of ways: (1) both have a dental formula, (2) both have large orbits, (3) both have small snouts. (a) However, not everyone agrees on the phylogenetic position of tarsier-like fossils such as Necrolemur (from Europe) and Rooneyia (from North America). iii) The eosimiids, from China and Burma, were once thought to be the ancestors of the anthropoids but they now appear to be the Asian branch of a diverse Eocene radiation of tarsier-like primates. iv) The evolution of true tarsiers is represented by a meager fossil record. (1) Fossils from the middle Eocene of Egypt and China and the late Eocene of Thailand indicate that the tarsier body plan has not changed very much. (2) The molecular evidence suggests that the five extant tarsier species diverged in the Miocene. e) Eocene and Oligocene early anthropoids i) Anthropoid origins are disputed. Molecular evidence indicates a 77 my time-depth for their origins. (1) Fossil anthropoids this old have yet to be discovered. (2) Most researchers support an African origin for the anthropoids, while others support an Asian origin. (3) The earliest undisputed anthropoid fossil is from the Middle Eocene of Algeria. ii) Most of the fossil evidence for early anthropoid origins comes from the Late Eocene and Early Miocene deposits of the Fayum Depression in Egypt. (1) Biretia is dated to 37 mya and Catopithecus is dated to 35 mya. V. Oligocene Primates a) Most of the Miocene Old World primate fossil record comes from the Fayum Depression, Egypt. b) True anthropoids of the Oligocene are placed in three families: the oligopithecids, parapithecids, and propliopithecids. i) The parapithecid genus Apidium, a squirrel-sized arboreal quadruped, is the most abundant of the t
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