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Primate Evolution

The fossil record of non-humanprimates

Cretaceous Period (135 - 65 m.y.a.)• Extremely active geological period

– Pangaea split into two segments by 125 m.y.a.• Northern land mass: Laurasia

– Included North America, Europe, Most of Asia– Rise of the Rocky Mountains

• Southern land mass: Gondwana– Included South America, Africa, Australia, Antarctica,

Indian subcontinent

– Worldwide climate much warmer than today sotropical and sub-tropical fossils are found farfrom the equator

Cretaceous Period 2• Floral Shift from gymnosperms to angiosperms

as dominant land plants– Gymnosperms are the vascular plants with seeds

that are not enclosed in an ovary (naked seeds),mainly the cone-bearing trees (ferns, ginkos,cycads, and conifers)

– Predominate from the Carboniferous period (about350 m.y.a.) when they began to displace the earliestspore-bearing land plants to the Cretaceous (about125 m.y.a.)

Cretaceous Period 3

– Angiosperms are the flowering plants, an advancedgroup of vascular plants with floral reproductivestructures and encapsulated seeds includingflowering herbs and trees, first appear near the endof the Mesozoic (135 m.y.a.)

• The flowering mechanism increased the potential forgenetic diversity (decreasing self pollination)

• Diversity of the angiosperms increased throughcoevolution with insect species, making for rapidadaptive radiation

Cretaceous Period 4

– During the Cretaceous angiosperms spread tobuild forests of increasing complexity, and tookover the dominant land plant role after the K/Textinction

– New econiches opened and old ones expanded• Frugivory: flowers and fruits are new food sources• Gramnivory: encased seeds from the new plants

• Insectivory: bugs that co-evolved with floweringspecies multiply increasing bug eating opportunities

Cretaceous/Tertiary Event

• Comet collisionrepresented by theChicxulub impact crateroff the north west coastof the Yucatan Peninsula– Combined effects of

terrestrial and marineimpact

– Dust and debris causecooling, break down offood webs

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K/T

• There is also a lot of volcanic activity on theDeccan Flats of the Indian subcontinent atthis time, adding to cooling

• > 50% of extant genera disappear at thistime– Terrestrial reptiles and marine invertebrates

most heavily affected– No land vertebrate larger than 50 pounds in

body weight survived the K/T

Primate Adaptation• Our Cretaceous ancestors were small, fuzzy

critters that were generalized enough in diet,morphology, and behavior to survive the K/Textinction

• Our primary adaptation at that time consisted ofthe “Good Luck” of being small, omnivorous,and behaviorally and ecologically flexible– Otherwise we would have gone the way of all large

bodied terrestrial vertebrates– This stochastic process appears to play a role in most

mass extinctions including the Permian and K/T

Epochs of the Tertiary Period,Cenozoic Era

Pleistocene 1.8 - 0.01 mya Ice Age

Pliocene 5 - 1.8 mya Hominid Radiation

Miocene 22.5 - 5 mya Hominoid Radiation

Oligocene 37 - 22.5 mya Anthropoid Origins

Eocene 53 - 37 mya First True Primates

Paleocene 65 - 53 mya Archonta Radiation

Paleoclimates

Whence come the Primates?

• Paleocene Placental Mammals:– No carnivores, rodents, modern herbivores– Primarily small, primitive insect eating animals

• Archonta (Superorder including Primates)– Plesiadapiformes: close relatives, possibly ancestral to

the Dermoptera (Colugo, Flying Lemurs)– Scandentia: Tree Shrews

– Chiroptera: Bats– Primates: Possibly including Purgatorius

Archonta

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Primate OriginsPrimate Family Tree

Living Critters

Anthropoid Origins

PaleoceneNon-Primate

Archonta

Scandentia(Tree Shrews)

Dermoptera(Flying Lemurs)

Chiroptera(Bats)

Plesiadapis rexfeeding on bugs in thetrees

Ignacius frugivorusfeeding on tree exudates

Picrodus silberlingifeeding on nectar in bushes

Chiromyoides minorfeeding on seeds

Mycrosyops elegansfeeding on bugs

Paleocene to Eocene Transition• Warming into the Eocene

– Warmest epoch of the Tertiary

• Wide ranging evergreen rain foreststhroughout North America and Europe

• Two cooling episodes broke the tropicality• From the mid-Eocene on there was a

gradual cooling and drying of the higherlatitudes

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EoceneContinentalConfigurationsand MigratoryPathways:A land bridgeconnected NorthAmerica and Europein the Early Eocenevia Iceland and theFaeroes and NorthAmerica and Asia viathe Bering Straight

Eocene Adaptations• First true Prosimians (Euprimates)• Primates spread with forested zones, appear to

adapt to preying on small, quick moving preyin arboreal settings (visual predation)– Grasping hands and feet– Nails instead of claws– Eyes rotated forward, enhanced stereoscopic vision– Elaboration of visual sensory pathways

Adapids versus Omomyids

Adapids,Omomyids, and

Anthropoids

Eocene to Oligocene Transition• Continued cooling, lowered sea level

– Extinction episode of many large bodied mammals atclose of Eocene

– Mid to high latitude vegetation changed dramaticallyfrom broadleaf evergreen rain forest to deciduousforests

• Remnant primates forced to cluster into smaller habitableforest areas near the equator (Fayum)

• Increased competition probably drove some changes inbehavior and adaptive patterns

– Habitats suitable for primates retreat into the currenttropics where most Oligocene primates are found

Paleoclimates

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Mid-Oligocene Extinction

• There is a mass faunal extinction event spanningabout 20,000 years at about 32 million years ago– Evident in the disappearance of archaic North

American land mammals• Potential Causes:

– Worldwide cooling and increased glaciation– Retreat of the Oceans– Floral changes related to Ocean circulation changes

• Catarrhines appear shortly after this extinctionEarly Oligoceneca. 35 m.y.a.

Apidium • 2-3 pounds• Arboreal quadruped• Fruit, seed eater• Very early and

primitive• Near split between

New World and OldWorld primates– Platyrrhine/Catarrhine

split

Aegyptopithecus

• 13 – 20 pounds (Howler monkey size)• Arboreal quadruped, slow climber• Frugivore, may have eaten some leaves• Very primitive, small brain, long snout• No derived characteristics of either

Cercopithecoids or Hominoids– May be close to the split between these groups

• Interesting degree of sexual dimorphism

Aegyptopithecuszeuxis

Propliopithecuschirobates

Apidiumphiomense

Origin of the Platyrrhini

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Origin of the PlatyrrhiniOligocene to Miocene Transition

• Warmer than the late Oligocene with highersea levels– Temperature peaks in mid-Miocene, about 15

m.y.a, then cools and climate becomes drier

• Continents were in nearly modern positions– Impact of India causes uplift in South Eurasia,

building Himalayan Mountains– African collision with Southwest Eurasia

causes rift valley system and allowed faunaldispersal

Miocene Fossil Ape Sites Miocene Hominoidea• Proconsulidae, early Miocene (Africa, Asia)

– Derived from Propliopithecids with larger bodiesand more modern molar morphology

– Proconsul• First Miocene ape described from Africa (1933)• 4 species ranging in size from 17 - 50 kg• Sexually dimorphic canines and frugivorous molars• Short limbs with monkey like proportions

– Quadrupedal and arboreal, but without suspensory abilitiesseen in living apes

• No tail-- like living apes

Juvenile Proconsul SkeletonJuvenileJuvenile ProconsulProconsul Miocene Hominoidea, 2

• Pongidae– Dryopithecus (mid to late Miocene, Europe)

• 20 - 35 kg, thin molar enamel, gracile canines, frugivore• Molar morphology is between Proconsuland Sivapithecus• Postcrania more like modern hominoids than that of any other

Miocene apes• Limbs suggest some suspensory ability

– Gigantopithecus (late Miocene to Pleistocene, Asia)• 2 species, 190 and 225 kg, largest known primate• Very thick mandible and broad molars, fibrous diet• Terrestrial locomotion?

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Dryopithecus Gigantopithecus

Miocene Hominoidea, 3

• Pongidae– Sivapithecus (late Miocene, Europe, Asia)

• 3 species from 40 - 90 kg• Thick molar enamel, low cusps, broad central incisors, seed

and nut eaters• Little canine dimorphism• Skull morphology very similar to living orangs—a likely

cousin• Quadrupedal rather than suspensory postcrania

– Ouranopithecus (late Miocene, Greece)• ca. 100 kg, Greek sites dated at 9 - 10 mya• Very thick molar enamel, relatively small canines• Wear analysis suggests a gritty diet like nuts or tubers• Facial morphology links to African apes and humans

Sivapithecus

Ouranopithecus Proconsulafricanus Dendropithecus

macinnesi

Limnopithecuslegetet

Proconsulnyanzae

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Ape AncestorsCatarrhine Cladogram

Molecular Clock