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Chapter 21
THE EVOLUTION OF PRIMATES
Paleoanthropologists study human evolution.
CHARACTERISTICS OF MAMMALS.
Mammals posses the following characteristics:
1. Endothermic: use metabolic energy to maintain constant body temperature.
2. Have hair.
3. Feed their young with milk produced by mammary glands.
4. Most are viviparous: the egg develops into a young inside the body of the mother.
5. Efficient respiratory system that uses the diaphragm for ventilation.
6. Four chambered heart.
7. Teeth are differentiated.
There are three groups of mammals:
1. Monotremes: mammals that lay eggs.
2. Marsupials: mammals that give birth to underdeveloped young and carry them in a pouch to
complete their development.
3. Placentals: give birth to more developed young, and have a placenta for nutrient, gas, waste
exchange, etc., between the mother and fetus.
Mammals appear in the Mesozoic about 200 m.y.a., and probably evolved from a group of therapsid
reptiles.
They remain an inconspicuous component of the fauna for about 150 million years.
PRIMATES.
Primates are mammals that appeared in the Cenozoic probably descendants from a small shrew-like
placental mammal that lived in trees and ate insects.
Distinguishing characteristics of Primates:
1. Well developed stereoscopic vision with enlarged, anteriorly directed eyes. Orbital rims entirely
enclosed by bone (all but most primitive).
2. Development of an opposable digit on the hand and/or foot. Increased mobility of digits and wrist.
3. Slender limbs that rotate freely at hip and shoulders.
4. Nails instead of claws; fleshy pads at the end of digits are very sensitive to touch.
5. Reduced snout, skull mostly posterior to orbits
6. Enlarged brain relative to body size.
7. Mammary glands reduced to two from several pairs.
8. Long postnatal growth period with parental care and long learning period.
Order PRIMATES
Semiorder STREPSIRHINI. Includes lemurs, galagos, and lorises.
Semiorder HAPLORHINI. Includes tarsiers, monkeys, apes and humans.
Suborder TARSIFORMES: tarsiers.
Suborder ANTHROPOIDEA: includes the monkeys, apes and humans.
The early anthropoids branched into two groups, the New and Old World monkeys.
New world monkeys are arboreal, have shorter thumb than Old World monkeys and in some cases the
thumb is absent; some have a prehensile tail.
Some Old World monkeys are quadrupeds, four-footed, and spend most of the time on the ground.
HOMINOIDS
Apes and humans are hominoids and arose from the Old World monkey lineage.
There are four modern genera of apes: gibbons, orangutans, gorillas and chimpanzees.
Hominoids are characterized by …
1. Their ability to brachiate with the corresponding skeletal adaptations: shorter and stiffer spine, more
flexible arms and shoulders, etc.
They are distinguished from monkeys by…
2.
3.
4.
5.
6.
7.
8.
9.
More vertical posture.
Larger and broader pelvis.
Attachments of internal organs for a more vertical posture.
No tail.
Five-cusp molars.
Scapula position allows arms to extend laterally.
Long postnatal care.
Complex social interaction.
Chimpanzees and gorillas are adapted to the ground.
They have kept the long arms of brachiating monkeys but use them in knuckle-walking.
HUMAN-APE COMPARISON
Humans are adapted to bipedal terrestrial locomotion and have…
1.
2.
3.
4.
5.
6.
7.
8.
9.
Longer hind limbs than forelimbs.
Free hands and refined manipulatory control.
Foramen magnum centered at the skull base.
Lack of supraorbital ridges.
Large brain relative to body size.
Small face.
Short canines.
Less body hair.
Other dental and skeletal features.
HOMINIDS consist of human and their ancestors.
PRIMATE FOSSIL RECORD
Cretaceous record absent. In the Tertiary:
Paleocene
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65-55 m.y.a.
Fossils of archaic primates called plesiadapiformes.
Eocene
55-35 m.y.a.
Two families of early prosimians were already present with an opposable thumb, a bony ring around the
optical orbits and nails rather than claws
Oligocene
35-24 m.y.a.
The anthropoid level was already present 30 m.y.a. Probably originated about 40 m.y.a. in the late
Eocene in Africa.
Aegyptopithecus from Fayum, Egypt is at least 31 m.y.a.
Miocene
25-5 m.y.a.
At least 30 different hominoids lived in the Miocene but most of them became extinct.
Dryopithecus may have given rise to modern apes and humans.
Dryopithecines were found in Africa, Asia and Europe.
Dates of divergence from hominids:
Gibbon 12 Million years
Orangutan 10 Million years
Gorillas 6 Million years
Chimpanzees 5 Million years (disagreement ranges from 7.7 to 3.5 m.y.a.)
Ardipithecus ramidus lived about 4.5 - 4.3 m.y.a. in what is now Ethiopia.
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Ape-like hominid.
Indication of an upright stance based on the position of the foramen magnum
A link between apes and hominids, e.g. gave rise to Australopithecus???
AUSTRALOPHITHECUS
The Southern Ape
Hominids that lived between 3.9 and 4.2 m.y.a. are assigned to the species Australopithecus anamensis.
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Presumably arose from Ardipithecus ramidus.
Upright stance and was bipedal.
Australopithecus afarensis is the earliest recognizable hominid fossil, 3.9 - 3.0 m.y.a.
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First fossil is known as "Lucy".
Just over a meter tall (3' 6"). Possibly a female?
Heavy brow, low forehead, prognathism, hominid-like teeth.
Australopithecus africanus (Taung child) from South Africa, was the first species to be found.
 Human-like similarities in teeth and brain.
 Adult brain was probably about 450 cc.
 Adult must have been smaller than a modern chimp.
 Bipedal: details of vertebrae, pelvis and lumbar curvature.
Homo habilis
 Fossils found in East and South Africa.
 2.3 m.y.a. in the Pliocene-Pleistocene boundary.
 Made stone tools.
Homo erectus
 Fossils from Java, China, Europe and Africa.
 2 m.y.a. to 250,000 y.a. (??).
 Used fire and made axes; full scale hunting of large game.
 Gradual increases in height and brain capacity.
 Some think that fossil of H. erectus represent two species: H. ergaster and H. erectus.
 H. ergaster might the ancestor of modern humans; H. erectus might be a dead end.
Intermediate fossil between H. ergaster and H. sapiens appear about 200,000 year ago showing cranial
capacity of 1,100 - 1,200 cc.
Homo sapiens
 The archaic H. sapiens (H. heidelbergensis) appeared about 800,000 years ago.
 Lived in Africa, Asia and Europe.
 Debate about having a monophyletic or polyphyletic origin from H. erectus.
 By 100,000 years ago Homo had reached the modern average cranial capacity of 1,300 - 1,500 cc.
 Skillful hunters.
Homo sapiens neanderthalensis or Homo neanderthalensis.
 Appeared about 230,000 years ago and lived to 30,000 years ago.
 Fossil found in Europe, Iraq and Africa.
 Sturdy build, receding chin and forehead, heavy brow ridges and jaw bones, larger front teeth, nasal
cavity with large triangular bony projections.
 They had achieved certain development of culture: ceremonies, burial of the dead, possibly religion
 Their disappearance is a mystery.
Homo sapiens sapiens
 Existed about 100,000 years ago.
 Homo sapiens sapiens began to replace Neanderthals about 40,000 years ago.
 The Cro-Magnon culture from France and Spain, exemplifies the early human.
 The origin of modern humans is controversial. There are two hypotheses:
1. Out of Africa
2. Multiregional
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Cultural evolution is the transmission of knowledge from one generation to the next.
1. Development of agriculture about 10,000 years ago.
2. Industrial Revolution.
3. Cultural evolution has resulted in large scale disruption and degradation of the environment.