Primate Evolution

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Primate Evolution

• Unit 5
• Chapter 16

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Primates (a group of mammals)

• majority live in trees (arboreal)
• include lemurs, monkeys, apes, and humans

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Primate characteristics

• Rounded heads
• Flattened faces
• Opposable thumb
• Binocular vision
• Flexible joints
• Full arm motion
• Some with prehensile tails
• Large brains

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Opposable thumb

• a thumb that can cross the palm to meet the other
  fingertips
• Adaptation gripping object

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Groups of primates
ancestral primates
Tarsiers and anthropoids
lemurs and ayes-ayes
Lemur Tarsier
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Lemurs and ayes-ayes

• Large eyes
• Nocturnal
• Habitat tropical rain forests
• Oldest found fossils 50-55 MYO

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Tarsiers and anthropoids

• Larger brains
• More upright posture
• Anthropoids include humans, apes, and monkeys.
• Humans and apes are in a group called hominoids.
• Monkeys are divided into two groups Old World
  and New World.

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New World monkeys

• Habitat rainforests of Central and South America
• Prehensile tail able to grasp and hold with this
  fifth limb

Squirrel monkey
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Old World monkeys

• Larger than New World monkeys
• Tails that are not prehensile
• Appear superficially to be like hominoid apes
  except that apes lack tails.
• Habitat diverse, including African savanna and
  Japanese mountains

Mandril
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Hominoid apes orangutans, gibbons, chimpanzees,
bonobos, and gorillas

• long, muscled forelimbs
• climbing in trees
• swinging from branches
• knuckle walking

Bonobo knuckle-walking
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Hominoid apes

• May be arboreal but mostly spends time on the
  ground
• Defined social structure and behaviors (including
  grooming)

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Hominoid humans

• Even larger brain capacity than apes
• Upright stature

Note the differences in brain capacity of the
skulls left to right, ape, chimp, human
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Where did hominoids come from?

• Scientists believed that Old World and New World
  monkey shared a common anthropoid ancestor.
• From DNA evidence, scientists believe this to be
  the order of ape evolution gibbons, orangutans,
  African apes, gorillas, and chimpanzees.

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Comparing DNA of humans and chimps

• Humans and chimps share the greatest sequence of
  DNA nucleotides.
• This implies that humans and chimps are more
  likely to share a recent ancestor.
• This does not imply that humans descended from
  chimps.

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Human evolution

• Fossil and DNA evidence indicates that about 5 to
  8 million years ago, an ancestral hominoid
  diverged into two pathways chimps and humans.
• Changes in food supply and climate favored those
  hominoids that could forage for food on land
  rather than in trees.

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Characteristics for non-arboreal primates

• Bipedal using two legs for upright walking
• Upright posture facilitates primate to see
  farther
• Bipedal hominoid primates are called hominids and
  include humans.

Bipedalism is a more adapted behavior than
knuckle-walking apes.
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How do scientists know that early hominids walked
upright?

• The opening in the skull where the spinal cord
  attaches shows how the head and spine are
  positioned.
• Anthropologist Raymond Dart discovered an early
  skull that appeared ape-like but had the spinal
  attachment position like modern humans.

Notice how the angle of the arrow changes with
the human skull as compared to the ape and chimp.
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Australopithecus africanus

• The skull that Dart discovered was named A.
  africanus.
• Estimated age 2.5 to 2.8 MYO
• These primates are called australopithecines
  (apelike and humanlike).

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1974 discovered australopithecine Lucy
Australopithecus afarensis, dated about 2-3 MYO,
shows pelvis structures that would indicate
bipedalism.
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Comparing skulls and pelvic bones
Chimps Early hominid Modern
human
Similar brain case size between these two
Shorter and wider pelvic bones indicate
bipedalism.
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Australopithecine extinction

• Fossil records indicate a disappearance about
  2.0-2.5 MYA.
• Hominids more like modern humans with larger
  brain cases may have evolved next.

In 1964, Louis and Mary Leakey discovered skulls
more like modern humans in Tanzania and named
this group Homo.
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Homo habilis

• handy man
• Ancient stone tools found near the fossils of H.
  habilis
• Estimated age 1.5-2.5 MYO

Examples of tools that H. habilis may have used
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Homo erectus may have evolved from H. habilis.
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H. erectus characteristics

• Larger brain than H. habilis
• More human-like face

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H. erectus

• Stone hand axe were found near H. erectus
  fossils, indicating they hunted.
• Hearths with charred bones found in H. erectus
  caves indicate that they may have used fire.

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H. erectus migration

• About 1 MYA, H. erectus migrated throughout
  Africa, Asia, and Europe.
• They became extinct between 130,000 and 300,000
  years ago.
• This is about the time that Homo sapiens fossils
  appear in the fossil record (100,000-500,000 YA).

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Neanderthals Homo group

• 35,000-100,000 YA in Europe, Asia, and Middle
  East
• Larger brain cases than H. erectus
• Prominent nose
• Thick bones
• May be a sister species to modern humans (not
  direct ancestor)
• Lived about the same time as Cro-Magnon

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Cro-Magnon early humans

• 35,000-40,000 YA
• Same height, skull structure, tooth structure,
  and brain size as modern humans
• Toolmakers and artists
• Language

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Possible appearance of Cro-Magnon
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Early humans crossing land bridge

• 12,000 years ago, evidence shows that they
  crossed a land bridge into North America.
• They built settlements and domesticated animals.

Modern coastline
Ancient coastline
Ice sheets 21,000 yrs ago
Ice sheets 12,000 yrs ago
Possible migration route