Lecture 6 primate anatomy and social behavior

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Lecture 6 Primate Anatomy and Social Behavior

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Lecture 6 primate anatomy and social behavior

  1. 1. Anthro 101: Human Biological Evolution Lecture 6: Primate Anatomy and Social Behavior
  2. 2. Basic primate phylogeny Lemurs, lorisesTarsiers ProsimiiAnthropoidea New World Monkeys Old World Monkeys Apes & humans Haplorhines Strepsirrhines Primates (Hominoidea)
  3. 3. Forms of Locomotion • Slow quadrupedal climbing • Vertical Clinging & Leaping • Arboreal & Terrestrial Quadrupedalism • Semi-brachiation • Brachiation • Knuckle walking • Bipedalism
  4. 4. Primate Skeleton - generalized http://www.bristol.ac.uk/centenary/look/cabinet/monkey.html
  5. 5. Skeletal features to note as you do the in-class activity: • Body position • Spine shape • Length & shape of trunk (torso) • Position of shoulder blade (scapula) • Limb length • Finger length (thumbs) • Length of tail
  6. 6. Intermembral Index • humerus + radius x 100 femur + tibia • hindlimbs vs. forelimb  longer in the part that does the most work • Bipeds & vertical clinging and leaping  hindlimb longer than forelimb • Quadrupeds  Approx equal lengths • Brachiators  forelimbs longer than hindlimbs
  7. 7. Slow quadrupedal climbing (prosimians) • Slow lorises of South Asia • Robust muscles & limb bones • Mobile ankle, wrist, hip • Short tails
  8. 8. Vertical clinging and leaping - prosimians • Vertical body  Orthograde • Push off branch with hindlimbs • Turn midair and land vertically again • Evolved two or three different times in prosimians • Bush babies • Sifakas • Lemurs Sifaka
  9. 9. Arboreal quadrupeds – monkeys • Arboreal - run & leap • Walk on palms on top of branches • Push off with hindlimbs • Stabilize with tail (long) • Pronograde (horizontal) posture • Longer fingers & toes to grab branch • Prehensile tails in NWM • No terrestrial species in NWM Owl Monkey Squirrel Monkey Diana Monkey
  10. 10. Semibrachiation • New World  Hands + prehensile tail • Old World  Hands, no tail use
  11. 11. Terrestrial quadrupeds - Old world monkeys • Lots of time on ground, but also in trees • Pronograde (horizontal) posture • Walks on palm/toes (shorter digits) • Move limbs in limited plane  (baboons, dogs) • Rarely hang full weight from arms • Shorter tail – not balancing • Barrel shaped rib cage baboon Mandrill © Robert Young
  12. 12. Brachiation - gibbons • Shoulder blade on the back rather than top of torso  Full range of arm motion • Cone-shaped rib cage • Long, curved fingers • Small thumbs • Long arms • Ball and socket wrist • No tail Siamang
  13. 13. Slow quadrumanous climbing - orangutans • Grasp branches with hands and feet as slowly move through trees • Females almost totally arboreal • males distance travel on the ground  Fist walking rather than knuckles • Brachiating ancestor  Longer arms than legs  Cone shaped torso  No tail  Long fingers
  14. 14. Knuckle-walking - chimps & gorillas • Great apes too large to brachiate frequently  Still use upper body & arms, suspend body when they do • Stronger wrists bones than brachiators in order to support weight on arms • Brachiating ancestors  Longer arms  Longer fingers  No tail  Scapula on back  Cone shaped torso Chimpanzee
  15. 15. Hominoids: Homininae: Hominini Bipedalism • Unique to humans (hominins) • Modifications to:  Pelvis  Knees & legs  Feet
  16. 16. Changes in the pelvis narrowly center our weight Human pelvis is a bowl  Supports internal organs  Short and broad ilium  Shorter ischium  abductor muscles attach to wide surface of ilium  Maintains the center of gravity over one foot while walking Chimp pelvis is longer and narrower  Organs “hang” below  Strong muscles on ischium
  17. 17. • “S-shaped” curves in spinal column keep trunk centered over pelvis • Lumbar curve • C-shaped curve in chimps more Changes in the spine center our weight over the pelvis
  18. 18. To walk efficiently, knees must be close to center line of body • Pelvis wider and shorter • Femur slants inward from wide pelvis • Close-knee stance • Centers weight for balance and efficiency (less muscle work to hold upright) • Long femur neck = more surface for abductor muscle attachment • Longer leg bones  Increased stride chimp human
  19. 19. • Arched foot  “spring”-like shock absorbers  Return energy to the next push  Heel-toe stride • Loss of opposable toe necessary to act as a platform for body - big toe in-line • Stiff foot makes better platform Bipedality also causes changes in the feet
  20. 20. Comparative anatomy of manipulation • Apes long curved fingers & short thumb  Hook over branches • Humans shorter fingers & longer thumb  Allows precision grip and greater opposability of hand  Bones in palm rotate more to allow finger tips to meet the thumb Human hand
  21. 21. Changes in the skull: Foramen magnum • Hole in skull where spinal cord and brain connect • Position indicates body posture • Nuchal ridge on back of skull (occipital bone) show where muscles attach Human skull is balanced on top!
  22. 22. Brain Size Lemur Howler monkey (NWM)  OWM
  23. 23. Features of the skull Prognathism Enclosed eye Orbits Dental arcade Diastema Canine size
  24. 24. Why do primates live in groups? • Benefits of group life • Costs of group life • Why do primates live in so many kinds of groups?  Balancing costs & benefits • How do:  Resources (diet), predators, climate, and “conspecifics” affect this balance?
  25. 25. 1. Why do primates live in groups? • Most mammals are solitary • Many prosimians solitary • Why are diurnal primates social?
  26. 26. Major benefits of group life • Protection versus predators • Better access to resources • Access to potential mates
  27. 27. Who likes primate snacks? leopard These guys do!
  28. 28. Some larger primates also like primate snacks Chimps hunt red colobus monkeys Baboons prey on vervets Humans kill primates, and sometimes eat them
  29. 29. We don’t see predation very often, but there are signs indicating why someone’s missing leopard paw print drag marks
  30. 30. Severe injuries are also likely caused by predators • Wound observed • Healthy animals disappear overnight Oryx, back wound Juvenile, scalp wound
  31. 31. For diurnal primates, living in groups is an effective anti-predator strategy = the Predation Model 1. Detection 2. Dilution 3. Defense
  32. 32. Detection: In larger groups, there are more eyes to watch out for predators
  33. 33. Dilution: In groups, any particular individual less likely to be caught by predator Imagine chance of being caught = 1/n, where n = group size   risk = 1/2             risk = 1/12            
  34. 34. Defense: Many strategies for diurnal primates • Sleep in trees, cliffs • Defensive weaponry • Large body size • Vigilance • Alarm calls • Mobbing • Interspecific associations
  35. 35. Nocturnal primates use different strategies • Hide during day • Park infants while feeding • Solitary • Quiet • Cryptic
  36. 36. Living in groups also has costs 1. Competition 2. Contagion 3. Cuckoldry 4. Inbreeding 5. Cannibalism 6. Infanticide
  37. 37. 2. Natural selection shapes social organization to balance the costs & benefits of group living • Socioecology = study of how ecological forces shape the size and structure of social groups
  38. 38. Solitary (but differentiated social relationships) Orangutan Loris • each individual lives alone, occasionally meet up for mating • may chose to neighbour with kin, meet more often
  39. 39. Monogamous (territorial pairs + offspring) Titi monkeys Gibbons
  40. 40. Mountain gorillas Black and white colobus One-male, Multi-female groups (polygyny)
  41. 41. Pygmy marmoset marmoset Callitrichids One-female, two-male groups (Polyandry)
  42. 42. Ring-tailed lemurs Savanna baboons Multi-male, multi-female groups
  43. 43. Spider monkeys Chimpanzees Communities (fission-fusion social organization)
  44. 44. Some argue that primates live in groups to better compete for resources = Resource Defense Model  Between group competition To understand competition you need to understand: • Diet – How big is the species? How much space is needed to find enough food? • Food distribution –Where & how does the food grow? • Female reproduction – Timing & Frequency? • Protection – Are males a threat to females & infants? Are males needed for protection? • Affect what kinds of groups primates will form and when
  45. 45. Body size affects required quality & amount of food in diet • Larger bodies need more food, but less energy per pound  can get enough by eating lots of lower quality leaves • Smaller bodies need less food, but more energy per pound  To get enough need smaller amount of high quality insects, fruit
  46. 46. The distribution of food affects the type of competition • Dispersed --> scramble competition  Food is distributed evenly  Food items not worth fighting over  Scramble to get enough food  no direct competition • Clumped --> contest competition  Resources are scarce & valuable  Resources are worth fighting over  Contest access to particular resources
  47. 47. Groups will form based on the species’ diet • Is a food defensible? If yes, then species will form groups that cooperate to defend food resources. • Larger groups will defend more successfully than small groups • Larger groups need more resources than small groups • Defend territories • Defend resources within homerange

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