Early Primate Evolution

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Early Primate Evolution

• Early Monkeys and Apes

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Early Monkeys and Apes

• The Oligocene Epoch was largely a gap in the
  primate fossil record in most parts of the world.
  
• This is especially true for prosimian fossils.
• Most of what we know about them came from the
  Fayum deposits in Western Egypt.
• While this area is a desert today, 36-31 million
  years ago (during the early and mid Oligocene) it
  was a tropical rainforest.
• Other Oligocene deposits containing some fossil
  primate bones have been found in North and West
  Africa, the southern Arabian Peninsula, China,
  Southeast Asia, as well as North and South
  America.

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• Monkeys evolved from prosimians during the
  Oligocene or slightly earlier.
• They were the first species of our suborder--the
  Anthropoidea.
• Several genera of these early monkeys have been
  identified--Apidium and Aegyptopithecus are the
  most well known.
• The former was about the size of a fat squirrel
  (2-3 pounds), while the latter was the size of a
  large domestic cat (13-20 pounds).
• Both were probably fruit and seed eating forest
  tree-dwellers.

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Aegyptopithecus zeuxisBelieved to be from the
earliest family of man. Cat-sized anatomical
features bridge prosimian primates and apes.
Based on 1966 Dr. Elwin Simons find.
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• Compared to the prosimians, these early monkeys
  had fewer teeth, less fox-like snouts, larger
  brains, and increasingly more forward-looking
  eyes.
• Due to the comparative scarcity of Oligocene
  Epoch prosimians, it is generally believed that
  the monkeys out-competed and replaced them in
  most environments at that time.
• Supporting this hypothesis is the fact that
  modern prosimians either live in locations where
  monkeys and apes are absent or they are normally
  active only at nighttime when most of the larger,
  more intelligent primates are sleeping.

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• The Oligocene was an epoch of major geological
  change with resulting regional climate shifts
  that likely affected the direction of evolution
  and altered fossil preservation conditions.
• By the beginning of the Oligocene, North America
  and Europe drifted apart and became distinct
  continents.
• The Great Rift Valley system of East Africa also
  was formed during the Oligocene along a 1200 mile
  long volcanically active fault zone between large
  tectonic plates.
• During the early Eocene Epoch, about 55,000,000
  years ago, India finally crashed into Asia and
  began forcing up the Himalayan chain of mountains
  and the Tibetan Plateau beyond.

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• By the Oligocene, the progressive growth of this
  immense barrier very likely altered continental
  weather patterns significantly by blocking the
  summer monsoonal rains.
• These and other major geological events during
  the Oligocene triggered global climatic changes.
  
• The cooling and drying trend that had begun in
  the late Eocene Epoch accelerated, especially in
  the Northern Hemisphere.
• A result was the general disappearance of
  primates from these northern areas.
• However, global climates were still warmer than
  today.

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• By the middle of the Miocene Epoch, the ongoing
  movement of tectonic plates created new mountain
  chains.
• These in turn altered local weather patterns.
• As a result, there were new selective pressures
  affecting primate evolution.
• Primate fossils are common from the Miocene.
• However, not all primates are equally represented
  in the fossil record.
• Apes apparently evolved from monkeys early in
  this epoch.
• Fossil monkeys and prosimians are comparatively
  rare from most of the Miocene, but apes are
  common.
• Apparently, apes at that time occupied some
  ecological niches that would later be filled by
  monkeys.

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• Among the Miocene primates were the ancestors of
  all modern species of apes and humans.
• By 14 million years ago, the group of apes that
  included our ancestors were apparently in the
  process of adapting to life on the edges of the
  expanding savannas in Southern Europe.
• They were very likely members of the genus
  Dryopithecus.
• Toward the end of the Miocene, less hospitable
  cooler conditions in the Northern Hemisphere
  caused many primate species to become extinct
  while some survived by migrating south into
  Africa and South Asia.
• About 9 million years ago, the descendents of the
  dryopithecines in Africa diverged into two
  lines--the gorillas and the line that would lead
  to humans and chimpanzees.
• Around 6 million years ago, another divergence
  occurred which separated the chimpanzees from the
  early hominids (human-like primates) that were
  our direct ancestors.

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Miocene Fossil Hominoids

• Continental drift during the Miocene altered
  climatic patterns and created new migration
  routes.
• The initial Miocene was warmer than the preceding
  Oligocene.
• The Arabian Plate docked with northeast Africa
  around 16 m.y.a., allowing African animals direct
  passage into southwest Asia.

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• There were more forms of hominoids during the
  Miocene (23-5 m.y.a.) than there are today.
• The Miocene hominoids may be grouped
  geographically into African, European, and Asian
  forms.
• The African forms (23-14 m.y.a) include the
  best-known genus Proconsul from Kenya.
• The European forms (16-11 m.y.a.) include a
  number of derived forms that are not well
  understood.
• The Asian forms (16-7 m.y.a.) are the largest and
  most varied group.
• The best-known genus is Sivapithecus.

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• African forms (23-14 mya)- Known especially for
  westerns Kenya, these include quite generalized,
  in many ways primitive, hominoids. The
  best-known genus is Proconsul.

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• Proconsul is one of the best represented Miocene
  hominoid in the fossil record.
• It lived from approximately 23 to 14 million
  years ago.
• From the full arrray of remains it has been shown
  that there was considerable variation in this
  genus.
• Body sizes ranged from that of a small monkey (10
  pounds) to that of a female gorilla (150 pounds).
  
• They also inhabited a wide range of environmental
  niches.
• This included open woodlands as well as dense
  rain forests and it is believed that perhaps some
  were partially terrestrial.
• They exhibit the typical Old World anthropoid
  dental pattern of 2-1-2-3.
• Proconsul also has the typical 5-Y pattern of
  cusps seen in the lower molars of hominoids.
• Their teeth also consist of a thin layer of
  enamel which suggests that they were probably
  fruit eaters.
• Brain size estimates show that their brains were
  as large or larger than contemporary Old World
  monkeys though probably not as large as
  contemporary hominoids.

Proconsul heseloni skull front view
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• European forms (13-11 mya)- known form widely
  scattered localities in France, Spain, Italy,
  Greece, Austria, and Hungary, most of these forms
  are quite derived.
• However, this is a varied and not well-understood
  lot.
• The best know of the forms are placed in the
  genus Dryopithecus the Hungarian and Greek
  fossils are usually assigned to another genera.
• The Greek fossils are called Oreopithecus and
  remain dated to sites 9 to 10 million years of
  age.
• Evolutionary relations are uncertain, but several
  researchers have suggested a link with the
  African ape/hominid group

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• The genus Dryopithecus includes a widespread
  group of Miocene, fossil pongids from Africa and
  Europe.
• There are both large and small forms in the
  genus, which was first described by Lartet in
  1856. The cast available is of a well researched
  reconstruction of D. major, an important species
  recovered from Kenya and Tanganyika in East
  Africa. D. major was a large species with a
  typically pongid-like cranium.
• The face is quite strongly protruding
  (prognathic), the dentiton substantial  and the
  canine teeth pointed and projecting well above
  the general tooth line.

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Oreopithecus bambolii
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• Asian forms (16-7 mya)- The largest and most
  varied groups from the Miocene fossil hominoid
  assemblage, geographically dispersed from Turkey
  through India/Pakistan into southern China.
• The best known genus is Sivapithecus (known from
  Turkey and Pakistan).

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Sivapithecus
Sivapithecus skull compared to a modern orangutan
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• There are 5 important generalizations regarding
  the Miocene hominoids.
• They are definitely hominoids.
• They are mostly large-bodied hominoids.
• Most of the Miocene forms are derived relative to
  living apes, and therefore dont make very good
  ancestors.
• Sivapithecus from Turkey and Pakistan has derived
  facial features that are similar to living
  orangutans.
• There are no fully documented, definite hominids
  among the Miocene material, although it now
  appears that hominids diverged in the latter
  Miocene.