Primate and Human Evolution

1. Chapter 19 Primate and Human Evolution

2. The Cradle of Mankind • Olduvai Gorge on the eastern Serengeti Plain, Northern Tanzania • is often referred to as “The Cradle of Mankind” • because of many important hominid discoveries there

3. Who are we? • Who are we? • Where did we come from? • What is the human genealogy? • These are basic questions • that we probably have all asked ourselves

4. Back Farther Than We Thought • Just as many people enjoy tracing • their own family history as far back as they can, • paleoanthropologists are discovering, • based on recent fossil finds, • that the human family tree goes back • much farther than we thought

5. Hope of Life • In fact, a skull found in the African nation of Chad, • in 2002 and named Sahelanthropus tchadensis • but nicknamed Tourmaï, • which means "hope of life" in the local Goran language, • has pushed back the origins of humans • to nearly 7 million years ago • Another discovery reported in 2006 • provides strong evidence for • an ancestor-descendant relationship • between two early hominid lines, • one of which leads to our own human lineage

6. Understanding in Flux • So where does this leave us, evolutionarily speaking? • At a very exciting time, as we seek to unravel the history of our species • Our understanding of our genealogy • is presently in flux, • and each new fossil hominid find • sheds more light on our ancestry

7. Human Evolution • Human evolution • is just like that of other groups • We have followed • an uncertain evolutionary path • As new species evolved, • they filled ecologic niches • and gave rise to descendants • better adapted to the changing environment • or they became extinct • Our own evolutionary history • has many “dead-end” side branches

8. New Hypotheses About Our Ancestry • We examine the various primate groups, • in particular the origin and evolution of the hominids, • the group that includes our ancestors • However, we must point out • that new discoveries of fossil hominids, • as well as new techniques for scientific analysis • are leading to new hypotheses about our ancestry

9. Continuing Discoveries Change Our Ideas • New discoveries may change • some of the conclusions stated here • Such is the nature of paleoanthropology— • and one reason why • the study of hominids is so exciting

10. What Are Primates? • Primates are difficult to characterize as an order • because they lack the strong specializations • found in most other mammalian orders • We can, however, point to several trends • in their evolution that help define primates • and are related to their arboreal, • or tree-dwelling, ancestry

11. Trends in Primates • These include changes in the skeleton • and mode of locomotion, • an increase in brain size, • a shift toward smaller, fewer, • and less specialized teeth, • and the evolution of stereoscopic vision • and a grasping hand with opposable thumb • Not all these trends took place in every primate group, • nor did they evolve at the same rate in each group

12. Variations • In fact, some primates • have retained certain primitive features, • whereas others show all • or most of these trends

13. Classification of Primates • The primate order is divided into two suborders • Prosimii and Anthropoidea • The prosimians, or lower primates, • include the lemurs, lorises, tarsiers, and tree shrews, • while the anthropoids, or higher primates, • include monkeys, apes, and humans

14. Classification of Primates • Order Primates: • Suborder Prosimii: (lower primates) Lemurs, lorises, tarsiers, tree shrews • Suborder Anthropoidea: (Higher primates) Monkeys, apes, humans • Superfamily Cercopithecoidea: Macaque, baboon, proboscis monkey (Old World monkeys) • Superfamily Ceboidea: Howler, spider, and squirrel monkeys (New World monkeys) • Superfamily Hominoidea: Apes, humans • Family Pongidae: Chimpanzees, orangutans, gorillas • Family Hylobatidae: Gibbons, siamangs • Family Hominidae: Humans

15. Prosimians • Prosimians are generally small, • ranging from species the size of a mouse • up to those as large as a house cat • They are arboreal, have five digits • on each hand and foot • with either claws or nails, • and are typically omnivorous • They have large, forwardly directed eyes • specialized for night vision, • hence most are nocturnal

16. Tarsier • Tarsiers are prosimian primates

17. Prosimians • As their name implies • pro means "before," and simian means "ape”, • prosimians are the oldest primate lineage, • and their fossil record extends back to the Paleocene • During the Eocene, prosimians were • abundant, diversified, and widespread • in North America, Europe, and Asia

18. Eocene Prosimian • Notharctus, a primitive Eocene prosimian • from North America

19. Prosimians Declined in Cooler Climate • As the continents moved northward • during the Cenozoic • and the climate changed from warm tropical • to cooler midlatitude conditions, • the prosimian population decreased • in both abundance and diversity

20. Prosimians Are Tropical • By the Oligocene, hardly any prosimians • were left in the northern continents • as the once widespread Eocene populations • migrated south to the warmer latitudes • of Africa, Asia, and Southeast Asia • Presently, prosimians are found • only in the tropical regions • of Asia, India, Africa, and Madagascar

21. Anthropoids • Anthropoids evolved from a prosimian lineage • sometime during the Late Eocene, • and by the Oligocene • they were a well-established group • Anthropoids are divided into three superfamilies

22. New World Monkey: Spider Monkey • New World Monkeys constitute a superfamily belonging to the suborder Anthropoidea (anthropoids)

23. Old World Monkey: Baboon • Another superfamily of the anthropoids: • the Old World monkeys

24. Hominoids: Chimpanzees • The honinoids, include apes and humans

25. Early History of Anthropoids • Much of our knowledge about • the early evolutionary history of anthropoids • comes from fossils found in the Fayum district, • a small desert area southwest of Cairo, Egypt • During the Late Eocene and Oligocene, • this region of Africa was a lush, tropical rain forest • that supported a diverse and abundant fauna and flora • Within this forest lived many different • arboreal anthropoids as well as various prosimians

26. Thousands of Fossil Specimens • In fact, several thousand fossil specimens • representing more than 20 species of primates • have been recovered from rocks of this region • One of the earliest anthropoids, • was Aegyptopithecus, • a small, fruit-eating, arboreal primate, about 5 kg • It had monkey characteristics and ape features • and is the closest link we currently have • to Old World primates

27. One of the Earliest Anthropoids • Skull of Aegyptopithecus zeuxis, • one of the earliest known anthropoids

28. Anthropoid Superfamilies • Anthropoids are divided into three superfamilies • Cercopithecoidea (Old World monkeys), • Ceboidea (New World monkeys), • and Hominoidea (apes and humans)

29. Classification of Primates • Order Primates: • Suborder Prosimii: (lower primates) Lemurs, lorises, tarsiers, tree shrews • Suborder Anthropoidea: (Higher primates Monkeys, apes, humans • Superfamily Cercopithecoidea: Macaque, baboon, proboscis monkey (Old World monkeys) • Superfamily Ceboidea: Howler, spider, and squirrel monkeys (New World monkeys) • Superfamily Hominoidea: Apes, humans • Family Pongidae: Chimpanzees, orangutans, gorillas • Family Hylobatidae: Gibbons, siamangs • Family Hominidae: Humans

30. Old World Monkey Attributes • Old World monkeys • superfamily Cercopithecoidea • include the macaque, baboon, and proboscis monkey • They are characterized by close-set, • downward-directed nostrils • like those of apes and humans • grasping hands, • and a nonprehensile tail

31. Old Word Monkey • Superfamily Cercopithecoidea • the Old World monkeys

32. Old World Monkeys Distribution • Present-day Old World monkeys • are distributed in the tropical regions • of Africa and Asia • and are thought to have evolved • from a primitive anthropoid ancestor, • like Aegyptopithecus, • sometime during the Oligocene

33. New World Monkeys • New World monkeys • superfamily Ceboidea • are found only in Central and South America • They are characterized • by a prehensile tail, flattish face, • and widely separated nostrils • and include the howler, spider, and squirrel monkeys

34. New World Monkey • New World Monkeys are members of the superfamily Ceboidea

35. No Contact • New World monkeys probably evolved from African monkeys • that migrated across the widening Atlantic • sometime during the Early Oligocene, • and they have continued evolving in isolation • to this present day • No evidence exists of any prosimian • or other primitive primates • in Central or South America • nor of any contact with Old World monkeys • after the initial immigration from Africa

36. Hominoids • Hominoids • superfamily Hominoidea • consist of three families: • the great apes • family Pongidae • which includes chimpanzees, orangutans, and gorillas • the lesser apes • family Hylobatidae • which are gibbons and siamangs; • and the hominids • family Hominidae • which are humans and their extinct ancestors

37. Hominoid Lineage • The hominoid lineage • diverged from Old World monkeys • sometime before the Miocene, • but exactly when is still being debated • It is generally accepted, however, • that hominoids evolved in Africa, • probably from the ancestral group • that included Aegyptopithecus

38. Climatic Shifts • Recall that beginning in the Late Eocene • the northward movement of the continents • resulted in pronounced climatic shifts • In Africa, Europe, Asia, and elsewhere, • a major cooling trend began, • and the tropical and subtropical rain forests • slowly began to change to a variety of mixed forests • separated by savannas and open grasslands • as temperatures and rainfall decreased

39. Apes Adapted • As the climate changed, • the primate populations also changed • Prosimians and monkeys became rare, • whereas hominoids diversified • in the newly forming environments • and became abundant • Ape populations became reproductively isolated • from each other within the various forests, • leading to adaptive radiation • and increased diversity among the hominoids

40. Migration of Animals Possible • During the Miocene, • Africa collided with Eurasia, • producing additional changes in the climate, • as well as providing opportunities • for migration of animals • between the two landmasses

41. Hominoid Relationships • Two apelike groups evolved during the Miocene • that ultimately gave rise to present-day hominoids • Although there is still not agreement • on the early evolutionary relationships among the hominoids, • fossil evidence and molecular DNA similarities • between modern hominoid families • is providing a clearer picture of the evolutionary pathways • and relationships among the hominoids

42. Dryopithecines • The first group, the dryopithecines, • evolved in Africa during the Miocene • and subsequently spread to Eurasia, • following the collision between the two continents • The dryopithecines were a group of hominoids that varied • in size, • skeletal features, • and life-style

43. Proconsul • The best-known dryopithecine and perhaps • ancestor of all later hominoids • is Proconsul, • an ape-like fruit-eating animal • that led a quadrupedal arboreal existence, • with limited activity on the ground • The dryopithecines were very abundant • and diverse during the Miocene and Pliocene, • particularly in Africa

44. Proconsul • Probable appearance of Proconsul, a dryopithecine

45. Sivapithecids • The second group, the sivapithecids, • evolved in Africa during the Miocene • and then spread throughout Eurasia • The fossil remains of sivapithecids • consist mostly of jaws, skulls, and isolated teeth • Body or limb bones are rare, • limiting our knowledge • about what they looked like • and how they moved around

46. Sivapithecids Ate Harder Foods • Sivapithecids had powerful jaws • and thick-enameled teeth with flat chewing surfaces, • suggesting a diet of harder foods such as nuts • It is clear from fossil evidence, • the sivapithecids were not involved • in the evolutionary branch leading to humans, • but were probably the ancestral stock • from which present-day orangutans evolved • In fact, one early genus, Gigantopithecus, • was a contemporary of early Homo in Eastern Asia

47. Two Lineages • Although many pieces are still missing, • particularly during critical intervals • in the African hominoid fossil record, • molecular DNA as well as fossil evidence indicates • that the dryopithecines, African apes, and hominids • form a closely related lineage • The sivapithecids and orangutans • form a different lineage that did not lead to humans

48. Hominids • The hominids (family Hominidae) • the primate family that includes present-day humans • and their extinct ancestors • have a fossil record extending back • to almost 7 million years • Several features distinguish them from other hominoids • Hominids are bipedal; • that is, they have an upright posture, • which is indicated by several modifications in their skeleton

49. Comparison of Locomotion • Comparison between quadrupedal and bipedal locomotion • in gorillas and humans • In gorillas the ischium bone is long • and the entire pelvis is tilted toward the horizontal

50. Comparison of Locomotion • In humans the ischium bone is much shorter • and the pelvis is vertical • Comparison between quadrupedal and bipedal locomotion • in gorillas and humans