Biological Anthropology/Unit 2: Non-human Primates/Primate Evolution

= Primate Evolution =

Most of the physical evidence examined in paleoanthropology (the study of ancestral primates) comes from fossils.

Fossils
How does something become a fossil?

Taphonomy
The study of what happens to organisms after they die is taphonomy.

Taphonomy is important when studying fossils, in order to undertstand the context of the fossil and the environment from which it came. Has the fossil been disturbed in any way? Has it been moved by water, scavenged by animals, etc?

Sometimes taphonomy is done with experimental methods.

Fossil dating
In order to understand a fossil, one must be able to date the fossil and reconstruct its environment.

There are several methodsfor doing this.

Reconstructing the paleoenvironment (paleoecology)
Paleoecology uses evidence in the fossil record to determine what the landscape may have looked like during the time that a particular primate lived there (remember, evolution is environmentally dependent!).

Paleobotany: is the study of fossil plants. For more on paleobotany, check out Dr. Robert Gastaldo's site: A Brief Introduction to Paleobotany.

Paleopalynology: is the study of fossil pollen

Phytoliths: fossilized plant cells

Geologic time
An interactive geological time machine

The Mesozoic: the origin of mammals

 * The Mesozoic era is known as "the age of the dinosaurs", due to their ecological dominance at the time
 * Several things happened at the end of this period that caused dinosaurs to go (mostly) extinct and led to a rise in the mammals
 * One of these was a rise in the number and diversity of angiosperms (flowering plants)
 * The other was the K-T boundary extinction
 * The basic idea is that, whatever the cause(s) of the extinction where -- they caused a massive climate change.

Beginning of the Cenozoic era: the Paleocene epoch (65 to 56 million years ago (mya))
Where did primates come from?

The three original hypotheses of how primates first came about.

New hypothesis

Plesiadapiformes


 * Flexible body, some had nails (not claws), bushy tail
 * Small brain, prognathic face (projecting or snout-like). diastema (gap) between the incisors and the premolars.
 * Similar in lifestyle to an opossum, ate fruit and insects
 * From North America and Europe
 * Ranged from mouse-sized to small monkey-sized (11 lbs)

Watch this really cool filmabout our little ancestors, the Plesiadapiformes, and how they're related to us. Click on the arrow next to "Watch First Primates".

Moreon the Plesiadapiformes

The Eocene epoch: true primates (56 to 34 mya)

 * Climate change (warmer, wetter, more rainforests and angiosperms)
 * The first true primates (about 50 mya)
 * North America, Europe, North Africa, the Middle East, and Asia

Two main families:


 * Adapids: ancestor of strepsirhines (AKA prosimians)
 * Omomyids: ancestor of haplorhines (AKA monkeys, apes, and humans)

Adapids


 * Found in North America, Europe, Asia, and Africa
 * Resemble lemurs
 * Forward-facing eyes, larger brain, less prognathic
 * Nails (not claws), opposable thumb (and big toes)
 * Flexible body
 * Ate more leaves

Adapids hit the news !

Omomyids


 * Found in North America, Europe, and Asia
 * More closely resemble noctural prosimians, especially tarsiers
 * Largest are around 1 kg
 * Nails (not claws)
 * Less prognathic, big eyes (close together), larger brain
 * Ate more fruits and insects

The Oligocene epoch: the monkey/ape divergence (34 to 23 mya)
The global climate shifted again during this time period (cooling and drying). There is a reduction in the amount of rainforests, with them restricting toward the equator, but an expansion of grasslands. So, there was an increase in terrestrial (ground) niches and a decrease in arboreal (tree) niches.

There are two possible ways that monkeys and apes diverged within the anthropoids.


 * Eosimiasin China

OR

in Egypt (around 36-32 mya)

Parapithecids 


 * A good example of these was Apidium
 * Size of squirrel, but more monkey-like
 * Quadruped (walked on all fours)
 * Dental formula 2-1-3-3 (so is possibly the platyrrhine or New World monkey ancestor)

Propliopithecids


 * A good example of these was Aegyptopithecus (pictured right)
 * More ape-like
 * Dental formula 2-1-2-3 (so is possibly the catarrhine or Old World monkey and ape ancestor)
 * Aegyptopithecus in the news!

More on the originsof New World Monkeys

The Miocene epoch: the Old World monkey/ape divergence (23 to 5 mya)
There were two climate shifts during this period, first there was a warm period with heavy forestation, followed by drier and cooler climates with decreasing forest and increased grasslands.

At this point, the Old World monkeys and apes split within the catarrhines. The fossils are from east Africa.

The ape ancestors had the following traits:


 * no tail
 * arboreal quadrupeds (limb structure was still monkey-like)
 * y-5 molars
 * Some good examples of these are: Proconsul, Sivapithecus (pictured right), and Gigantopithecus

The Old World monkey ancestors at this point in time had the following traits:


 * A tail
 * Had macaque-like faces
 * Were medium sized 7-11 lbs
 * A good example of these is: Victoriapithecus