Origin of Primates

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					Origin of Primates

Biological Anthropological by Stanford, Allen, Anton Professor Bender

Mesozoic and beyond
 During Mesozoic era mammals diversified and became

more complex
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Because angiosperms, diversified just before leading to pollination by insects
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More insects, more seeds and fruits

 “Crater of Doom” End of Mesozoic
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Probably arising from an asteroid or comet crashing into the surface of the Earth (Chicxulub in Yucatán Peninsula)
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Led to extinction of the dinosaurs, Impact probably caused a firestorm and number of tidal waves, Led to abrupt global cooling, Combination of fire and cold killed much of the terrestrial life at the time Killed herbivorous dinosaurs then the carnivorous dinosaurs that preyed on them, The absence of large prey animals favored small,
insect-eating mammals over the larger dinosaur

After: changes in the paleocene
 Plesiadapiforms  Either separate mammal or suborder of primates
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Mainly in N. America and Europe and China
Controversy: More primitive than any living primate
     Small brains Prognathic face Eye sockets on side, not front, of face Postorbital bar – bony ring encircling the eye Large, rodent-like incisors that were separated from the premolars by a large diastema (gap between their anterior teeth)  Some had claws not nails  Lacked an opposable big toe

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Range from early Paleocene to the late Eocene
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What factors favored Primates?
 Paleocene was warmer than today and was a period

of recovery from the giant impact
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Flowering plants evolved, Insects increased in number and diversity

 We know that living primates emphasize vision over

olfaction and have tactile pads on their fingers, not hard pads and claws
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Tree living versus ground?

 Fossil record of early protoprimates (i.e.

plesiadapiforms) has helped to understand that early primate forebears probably were visual predators
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Dependent on sighting and catching insects to survive rather than clambering on branches for fruit

Early primate of the Eocene
 Climate warmed significantly at beginning of Eocene (54 mya)

resulting in the replacement of the archaic mammals of the Paleocene by the first representatives of a number of modern orders of placential mammals, including primates  First true primates, those that possess the bony characteristics by which identifying living primates
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Origin of strepsirhine-haplorhine split

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These are seen as true primates because they possess the full suite of primate traits
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Slightly larger brains Eye sockets positioned on the front of the face Complete postorbital bar Opposable big toe, Nails
 Reduction of snouts and whiskers suggests smell is less important

Adapoids (Strepsirhine Ancestors)
 Fossils suggests lemurs and lorises diverged

around 45 mya
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Adapoids – slow-moving arboreal quadrupeds that were active by day and probably ate fruit and leaves
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While found in both old and new world mainly found in old world Long broad snouts with teeth suggest some may have eaten a fibrous diet Eyes indicate some were probably nocturnal, others diurnal Postcrania indicate a diverse range of locomotion from leaping to quadrupedal climbing

Omomyoids (Haplorhine ancestors)
 Split from adapoids and may have given rise to

common ancestor of both tarsiers and anthropoids
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Smaller-bodied primates 1 oz to 5lbs
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Ate diets of insects and fruit and had larger orbits, probably for a nocturnal lifestyle

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Limb bones probably were evolved for active arboreal quadrupedalism and leaping, as indicated by the anatomy of hind leg and ankle bones Occurred both in Europe & North America
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54 to 34 mya North America and Europe linked by band of land and was similar

climate

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Eye sockets < than tarsiers

Selective pressures favoring split
 Clues from anatomy such as relative snout length and the shape

of their teeth suggest that adapoids and omomyoids divided up the available food resources, thus avoiding competition  Adapoids ate leaves and relied more on their sense of smell (longer snout)  Omomyoids focused on fruit and insects and had a shorter snout  Evolution of higher primates  The earliest higher monkeys are generalized monkeys that probably gave rise to all later higher primates  Early apes appeared in Miocene and were also more generalized than their living descendants and more diverse.  The initially diverse apes decreased in abundance through time, while monkeys became more abundant

The first monkeys?
 All higher primates (monkeys, apes, and humans) share certain

anatomical characters  Including: greater enclosure of the orbits, smaller snouts, fewer teeth, and a fused frontal bone and a fused mandible and larger body size
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These anatomical changes signal changes in the foraging habits of these primates, probably catalyzed for the changing environmental conditions

 Parapithecidae diverse group of early anthropoids
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Includes Apidium (resembling South American squirrel monkey)
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Eating seeds and fruit, Weighs approximately 2.2 lbs Leaping and running from trees on all fours

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Possessed 3 premolars suggesting it predated the split between New World monkeys (3) and Old World (2)

The first monkeys?
 Oligopithecidae diverse group of early anthropoids  Weighs approximately 1.8 to 3.3 lbs  Quadrupedal monkeys that lived in the trees  Ate insects and fruit  Combined primitive strepsirhine-like molars with the earliest known records of more advanced features such as a fused frontal bone and postorbital closure,  2:1:2:3 (incisors, canines, premolar, molar) dental formula  Propliopithecidae  Largest weighs approximately 13 to 15 lbs  Most advanced of early anthropoids  Looked something like the howler monkey in South America  Slow moving from branch to branch in search of leaves  2:1:2:3 (incisors, canines, premolar, molar) dental formula

New World monkeys
 Molecular evidence shows New World and Old World

monkeys diverged 40 mya but fossils from South America have only been found back 30 mya  South America was island continent and connection between it and Central/North America (Panamanian Isthmus) only formed 5 mya
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Were these monkeys:
 Advanced Eocene strepsirhines in North America  Or from most primitive anthropoids of Africa

 New World monkeys have 3 premolars not 2, linking

them to Apidium, a fossil monkey from Egypt  Ancestor could have “rafted” over

Old World monkeys
 According to DNA Old World monkeys and apes

shared a common ancestor about 25 MYA
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Fossils show ancestor had traits shared by both monkeys and apes
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Bony ear tube, Presence of 2 rather than 3 premolars Lacked bilophodont molars of Old World monkeys Lacked suspensory shoulder of modern apes

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Plio-Pleistocene radiation of African Old World monkeys is based on fossils collected from sites more famous for their hominid finds These monkeys were more diverse in terms of their body size, locomotion, and dietary habits than monkeys are today
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Appeared to have formed distinct communities in eastern and southern areas of Africa
 Some adapted for life in trees others apparently lived on the ground

What favored anthropoids origins?
 Primates were eating tough objects and their bodies were

growing bigger  Skulls were changing, mandible becoming a single bony unit, as did the frontal bone, and the orbits were becoming completely enclosed by bone
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These monkeys were successful because they were able to chew a tougher diet and better protect their eyes

 The earliest apes
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Living ape species are limited in number and fit into four genera
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Hylobates (the gibbons and Siamangs) Pongo (the orangutan) Gorilla (the gorilla) Pan (the bonobo and common chimpanzee)

The earliest apes
 Hominoid primate record reveals a diverse succession of

adaptive radiations  Appearance of dental apes – apelike teeth but with monkeylike postcranial skeletons  Molecular evidence suggests monkeys and apes diverged 25 mya  Fossil apes first appear 23 to 16 mya  Hominoids were almost completely restricted to Africa
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Unlike today, at that time Africa was uninterrupted expanses of forest and moist woodland
 Uplifting and rifting that dominate eastern Africa today had not yet occurred nor had the climatic divisions of arid and wet zones

 Only Old World monkeys possess specialized, high-crested

bilophodont molars for shearing leaves

The earliest apes
 All apes possess molars with five rounded cusps, connected by

a pattern of Y-shaped fissures or grooves (Y-5)  Dental apes were:  Small-bodied compared to modern apes,  Lacked suspensory shoulder,  Walked in plantigrade fashion, on the soles of their feet rather than on their knuckles  Around 17 MYA first evidence of land connection between Africa and Eurasia
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Connection allowed hominoid primates to migrate outside of Africa for the first time, and small, gibbon-like forms appeared in China
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Environmental changes show Africa starting to become drier

 Around 14 MYA the African great ape and human lineage

diverged from the Asian great ape lineage (the orangutans)

The earliest apes
 Around 11 to 5 mya large-bodied hominoids diversified and

dispersed into Europe and Asia
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In 1930s, German paleotologist Ralph von Koenigswald searched for fossils in drugstores as well as field  Gigantopithecus known most from jaws and teeth was enormous (>660 lb) and coexisted with Homo erectus
 Bones and teeth (enormous molars) used in traditional East Asian medicine  Largest to ever live ate a rough, fibrous diet, perhaps even bamboo

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Oreopithecus , around 7-8 MYA, swampy environment in Italy  Bipedal based on reconstruction of creature’s feet which were shaped almost like tripods in life, Divergent big toe and four other toes that were aligned in
nearly the opposite direction  Evolved in isolated habitat of a Mediterranean island that lacked predators, leading to adoption of a strange and awkward way of walking  Featured unique molar cusps and crests (ate leaves)

 Little fossils from the late Miocene (8-9 mya)
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Lack of fossils is related in part to the tropical forests in which apes live, moist places where biological processes often lead to the complete destruction of the skeleton

Selective pressures
 Miocene hominoids provide a picture of the ape and human

family tree before it was so drastically pruned back to just the few branches that exist today
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Monkeys and apes differ in mode of locomotion so the origin of hominoids probably is related in part to this  Brachiation – used by lesser apes, earliest form
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Arm positioned well lateral of the midline Wide thorax evolved (and longer clavicles, or collarbones) Since arm is often overhead, head is rounder Shape of scapula is changed – rotated onto animal’s back from the side and elongated in the direction of head and tail

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Brachiation evolved when more tree dwelling  As weather changed apes evolved to knuckle-walking for more terrestrial life First shift was dietary  Based on cooling of the environment and breaking up of the habitats  Monkeys focused on leafy diet with apes on fruits  Later apes, i.e. gorillas, return to a fibrous diet

The monkey’s tale
 At the middle of the Miocene apes were

abundant and monkeys fairly rare
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After mid-Miocene it’s a monkey’s world
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World got drier and colder R-selected versus K-selected (monkeys more R than apes)

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Only one group of apes seems to have overcome the issues of locomotion and reproduction to move into new, more open habitats (lineage became humans)

Molecular evolution in primates
 Molecular clock – systematic accumulation of genetic

differences through time (LCA)
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Calibrated with a fossil that corresponds with one of the nodes in the tree Rate constancy in the molecular code that is consistent for any protein or gene

 Relative rate test – comparision of the amount of genetic

differences between each primate species of interest and a member of an outgroup, such as a dog  Primate molecular phylogeny
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Goodman created local molecular clock based on more than 60 primate species calibrated from the fossil record  Places last common ancestor (LCA) of all primates at 63 mya  Deepest split of primates strepsirhines-haplorhines

Molecular phylogeny & human orgins
 Based on Ramapithecus hominid line originated

about 15 mya  Using phylogeny and albumin (immunolofical method) Sarich and Wilson date for the origins of hominids of 5 mya
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We are more closely related to African great apes than other great apes (orangutan) Was hotly debated for many years until genetic testing proved true  In earlier hominoids things like tooth enamel increase and decrease as the environment change


				
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