fossils, early primates, & anthropoid origins

fossils

• remains turned into rock through chemical replacement

• burial ideally soon after death

• within sedimentary rock and volcanic ash

factors that can impact fossilization

• rapid burial

• bone density, mineral content

• environment, size

• natural forces, erosion

taphonomy

• study of what happens to remains after death

• helps interpret fossil record

• looks at damage; trampling, abrasion, tooth marks

three major eras

• paleozoic

• mesozoic

• cenozoic

key epochs: cenozoic era (age of mammals)

• paleocene: first primate-like ancestor

• eocene: first true primates, prosimian-like

• oligocene: major primate evolution, age of monkeys

• miocene: early apes

• pliocene: first bipedal primates

• pleistocene: hominin evolution, appearance of genus homo

• holocene

3 early primates

• plesiadapiforms

• adapids

• omomyids

3 theories of primate origins

• arboreal theory

• visual predation hypothesis

• angiosperm radiation hypothesis

arboreal theory

• tree life drove primate traits

• increased vision, decreased smell, shorter snout

• grasping hands/feet, nails

• larger brain for hand-eye coordination

  • critiques: many mammals live in trees without primate traits

  • arboreal environment alone may not explain primate specializations

visual predation hypothesis

• traits evolved for hunting insects in trees

• binocular vision → depth perception

• prehensile hands → grasp prey

• more cortex → motor/visual control

angiosperm radiation hypothesis

• flowering plants → new niches

• primates evolved to exploid fruits, nectar, gums

  • problem: angiosperms older than primates

earliest primate adaptations

• shrew/rodent like, small

• claws, not nails

• lateral orbits

• long snout

• no post-orbital bar

plesiadapiforms

• 65 mya

• reduced shearing → omnivore

• ever-growing incisors

• “archaic primates”

3 key genera

• plesiadapis: rodent-like incisors, small brain, claws, no post-orbital bar

• purgatorius: earliest primate, shrew-like

• carpolestes simpsoni: transitional form

eocene primates

• plesiadapiforms extinct → adaptive radiation of prosimians

• first modern mammal orders

two major families of eocene

• omomyids

  • tarsier-like

  • small, short snout, large orbits → vision

  • NA, europe, asia

• adapids

  • lemur-like

  • longer snout, smaller orbits → smell

omomyid and adapid difference from plesiadapiforms

• larger brains

• post-orbital bar

• nails on digits

• no rodent incisors

early anthropoids in the late eocene

• fused frontal bone

• post-orbital closure (instead of bar)

• reduced olfaction, forward-facing eyes

• bigger brains

• nails not claws

two key species of early anthropoids

• eosimias (dawn monkey) in china

• biretia in egypt

three families found in fayum depression in egypt

• oligopithecids

• parapithecids (monkey-like, 3 premolars like NWM)

• propliopithecids (ape-like, 2 premolars like OWM)

  • aegyptopithecus = early catarrhine

aegyptopithecus traits

• 13-18 lbs

• sagittal crest

• dimorphic canines

• 5-Y molars

• frugivore

• convergent orbits

• snout suggests some olfaction

• equal-limb quadruped

new world primate origins: branisella

• bolivia, 26 mya

• oldest platyrrhine

• 3 premolars

• 3 molars with extra cusp

• how they reached s. america debated

miocene anthropoids: early miocene

• proconsul

  • 18 mya

  • ape-like teeth (Y-5), large incisors

  • no tail

  • quadrupedal but flexible

  • early hominoid

middle miocene

• kenyapithecus

  • 16-10 mya

  • molars resemble modern hominoids

late miocene apes

• migration from africa → europe and asia

• two major groups:

  • sivapithecus

    • orangutan ancestor

    • thick enamel skull similar to orangutans

    • large body

  • dryopithecus

    • suspensory, Y-5 molars

    • arm/hand proportions like modern apes

• ouranopithecus

  • greece

  • thick enamel, robust face

  • traits similar to australopithecine ancestors

• gigantopithecus

  • over 10ft tall ~600 lbs

  • sometimes linked to yeti/bigfoot