Early Hominid Evolution and Bipedalism Unveiled

1. Early hominid origins and evolution: the roots of humanity Chapter 7

2. Introduction • Charles Dawson found a fossil that he said was the “missing link” • It had a human skull and an ape jaw • Called Piltdown Man • It was a hoax (human skull fused with an orangutan jaw) • Shows people (wrongly) thought human ancestors were hybrid ape-men

3. What Separates Humans? • It is not big brains • It is bipedalism • We began walking bipedally 7 mya (million years ago) • We got big brains only 2 mya

4. Classification • Please remember: • Hominids are ancestors of any apes • Hominins are ancestors of humans

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6. bipedalism • Historically, scientists believed the identifiable feature of human ancestors was big brains • This was not supported in the fossil record • How would we tell bipedalism from a fossil?

7. Classification • Also remember that humans go in the ape classification of Hominoid • Why?

8. Classification • Also remember that humans go in the ape classification of Hominoid • Why? • Y-5 molar • No tail • Shared DNA

10. Bipedal adaptations • 1. foramen magnum underneath skull • 2. short, wide pelvis • 3. long legs • 4. no opposable big toe • 5. double-curved spine

11. Bipedal adaptations

12. Other hominin features • Honing canine: apes’ canines cut and shred food and are large and dangerous and they have a diastema. • Humans have small, nonhoning canines and no diastema • Apes have powerful chewing muscles and a sagittal crest for extra power. Humans are weak chewers • Why? What invention did human ancestors have that made food processing easier?

13. Other hominin features

14. bipedalism • It is hypothesized that our ancestors were knuckle-walkers, which allowed for easier upright standing • Climate and environmental changes may have selected for bipedalism

16. Why did bipedalism evolve? • Darwin’s Hunting Hypothesis: because of similarities between humans and apes, he concluded Africa must be our origin. There must have been something to shift us to walking on the ground • Unique human traits: • Bipedal vs quadrupedal • Tiny canines vs large canines • Tool use vs no tool use • Big brains vs smaller brains

17. Why did bipedalism evolve? • Darwin’s Hunting Hypothesis: Darwin asked what advantages bipedalism had and he concluded it freed the hands for holding weapons • We now know that we walked many millions of years before tools were made, but his hypothesis laid the foundation

18. Why did hominins evolve? • Another hypothesis involved the forest becoming fragmented, and hominids walking on two legs in between patches of trees. • Used less energy • Could see predators • Could hold things with hands • Less of the body in direct sunlight

19. Why did hominins evolve? • Owen Lovejoy’s Provisioning Hypothesis: heavy parental investment by mothers led to bipedalism • Males would better provision females if bipedal (free hands to carry more food) • Better infant survival and higher fitness for mother • Small level of sexual dimorphism in fossils supports this (cooperation of male and female pair…not males fighting for one female)

21. Benefits and costs of bipedalism • Pros: • Can carry things (frees hands) • Can see predators • Can save energy • Cons: • We are slow • If carrying items, makes us easy targets • Back injuries • If injure a foot, very difficult to get around

22. Who were the first hominids? • Pre-Australopithecines • Australopithecines • Paranthropus

23. Early hominins in east africca • Rift Valley • Volcanic rock • What dating technique?

24. Pre-australopithecines • Sahelanthropus tchadensis: earliest ancestor/oldest biped • “Chad Man” • 7-6 mya • Central Africa (Chad) • Small brain (350 cubic cm, cc) • Bipedal (foramen magnum) • Nonhoning canine • Close to the divergence of human line from ape line

25. Pre-australopithecines • Sahelanthropus tchadensis

26. Pre-australopithecines • Orrorin tugenensis: • “Original Man” • 6 mya • Mostly femurs (thigh bone) • Show bipedalism • Nonhoning canines

27. Pre-australopithecines • Aridpithecus ramidus: • “Great-grandma” • “Ardi” • 4-6 mya • Bipedal • All species so far still spent time in the trees…why? • May be direct ancestor to Australopithecines

28. Pre-australopithecines • Aridpithecus ramidus:

29. australopithecines • Australopithecines: • Hundreds of fossils from at least 7 species • Not 100% sure of all the relationships

30. australopithecines • Australopithecus africanus: • Raymond Dart found a small skull in a cave • “Taung Baby” • 4-3 mya • Thought baby ape at 1st • Small teeth, bidpedal foramen magnum • Later adult fossils had small canines too • *Showed that bipedalism came way before big brains*

31. australopithecines • Australopithecus africanus:

32. australopithecines • Australopithecus afarensis: • Kenya and ethiopia • 3 mya • Best-known and best-represented • “Lucy” over 40% of skeleton (but over 80% because skeleton is symmetrical) • If Ardi is great-grandma, Lucy is grandma • Foramen magnum, pelvis, legs, and feet all bipedal • Curved fingers (why?) • Small brain still (430 cc)

33. australopithecines • Australopithecus afarensis: • Smaller canines • Laetoli Prints: fossilized footprints in volcanic ash (how would you date these??) • Showed bipedalism and ‘first family’ (2 adults, 1 child)

34. australopithecines • Australopithecus afarensis:

35. australopithecines • Australopithecus:

36. australopithecines • Beginning 3mya, two lines of hominin evolution occurred, each with unique adaptations • One line went extinct and one line led to genus Homo

37. paranthropus • This next group is the second line that went extinct • Some still call this group “robust” Australopithecus but there are enough differences that I split them into a new genus Paranthropus • Paranthropus: • 2.5 mya • Larger, more robust bodies but small brains • Sagittal crest • Huge molars for crushing tough food • Flaring face • Do we have these adaptations? • Specialized food source may have led to extinction

38. paranthropus • Paranthropus:

39. PARANTHROPUS Differences • Biped • Robust • Small brain (smaller than A.) • Flared head • Sagittal crest • Large molars • Specializeed, tough diet AUSTRALOPITHECUS Biped Slender Small brain Rounder head Smaller teeth Varied diet

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