Primate Evolution Cretaceous Period (135

Cretaceous Period (135 - 65 m.y.a.)
• Extremely active geological period
Primate Evolution
– 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
The fossil record of non-human
primates
• Southern land mass: Gondwana
– Included South America, Africa, Australia, Antarctica,
Indian subcontinent
– Worldwide climate much warmer than today so
tropical and sub-tropical fossils are found far
from 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 (about
350 m.y.a.) when they began to displace the earliest
spore-bearing land plants to the Cretaceous (about
125 m.y.a.)
Cretaceous Period 4
– During the Cretaceous angiosperms spread to
build forests of increasing complexity, and took
over the dominant land plant role after the K/T
extinction
– 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 flowering
species multiply increasing bug eating opportunities
Cretaceous Period 3
– Angiosperms are the flowering plants, an advanced
group of vascular plants with floral reproductive
structures and encapsulated seeds including
flowering herbs and trees, first appear near the end
of the Mesozoic (135 m.y.a.)
• The flowering mechanism increased the potential for
genetic diversity (decreasing self pollination)
• Diversity of the angiosperms increased through
coevolution with insect species, making for rapid
adaptive radiation
Cretaceous/Tertiary Event
• Comet collision
represented by the
Chicxulub impact crater
off the north west coast
of the Yucatan Peninsula
– Combined effects of
terrestrial and marine
impact
– Dust and debris cause
cooling, break down of
food webs
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Primate Adaptation
K/T
• There is also a lot of volcanic activity on the
Deccan Flats of the Indian subcontinent at
this time, adding to cooling
• > 50% of extant genera disappear at this
time
– Terrestrial reptiles and marine invertebrates
most heavily affected
– No land vertebrate larger than 50 pounds in
body weight survived the K/T
Epochs of the Tertiary Period,
Cenozoic Era
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
Pleistocene
Whence come the Primates?
• Our Cretaceous ancestors were small, fuzzy
critters that were generalized enough in diet,
morphology, and behavior to survive the K/T
extinction
• Our primary adaptation at that time consisted of
the “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
Paleoclimates
Archonta
• 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
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Primate Origins
Living Critters
Primate Family Tree
Chiroptera
(Bats)
Anthropoid Origins
Dermoptera
(Flying Lemurs)
Paleocene
Non-Primate
Archonta
Scandentia
(Tree Shrews)
Plesiadapis rex
feeding on bugs in the
trees
Picrodus silberlingi
feeding on nectar in bushes
Ignacius frugivorus
feeding on tree exudates
Mycrosyops elegans
feeding on bugs
Paleocene to Eocene Transition
• Warming into the Eocene
– Warmest epoch of the Tertiary
• Wide ranging evergreen rain forests
throughout North America and Europe
• Two cooling episodes broke the tropicality
• From the mid-Eocene on there was a
gradual cooling and drying of the higher
latitudes
Chiromyoides minor
feeding on seeds
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Eocene
Continental
Configurations
and Migratory
Pathways:
A land bridge
connected North
America and Europe
in the Early Eocene
via Iceland and the
Faeroes and North
America and Asia via
the Bering Straight
Eocene Adaptations
• First true Prosimians (Euprimates)
• Primates spread with forested zones, appear to
adapt to preying on small, quick moving prey
in 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
Paleoclimates
• Continued cooling, lowered sea level
– Extinction episode of many large bodied mammals at
close of Eocene
– Mid to high latitude vegetation changed dramatically
from broadleaf evergreen rain forest to deciduous
forests
• Remnant primates forced to cluster into smaller habitable
forest areas near the equator (Fayum)
• Increased competition probably drove some changes in
behavior and adaptive patterns
– Habitats suitable for primates retreat into the current
tropics where most Oligocene primates are found
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Mid-Oligocene Extinction
• There is a mass faunal extinction event spanning
about 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 extinction
Apidium
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2-3 pounds
Arboreal quadruped
Fruit, seed eater
Very early and
primitive
• Near split between
New World and Old
World primates
– Platyrrhine/Catarrhine
split
Early Oligocene
ca. 35 m.y.a.
Aegyptopithecus
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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
Origin of the Platyrrhini
Aegyptopithecus
zeuxis
Propliopithecus
chirobates
Apidium
phiomense
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Origin of the Platyrrhini
Oligocene to Miocene Transition
• Warmer than the late Oligocene with higher
sea 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 faunal
dispersal
Miocene Hominoidea
Miocene Fossil Ape Sites
• Proconsulidae, early Miocene (Africa, Asia)
– Derived from Propliopithecids with larger bodies
and more modern molar morphology
– Proconsul
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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 abilities
seen in living apes
• No tail-- like living apes
Juvenile Proconsul
Juvenile Proconsul Skeleton
Miocene Hominoidea, 2
• Pongidae
– Dryopithecus (mid to late Miocene, Europe)
• 20 - 35 kg, thin molar enamel, gracile canines, frugivore
• Molar morphology is between Proconsul and Sivapithecus
• Postcrania more like modern hominoids than that of any other
Miocene apes
• Limbs suggest some suspensory ability
– Gigantopithecus (late Miocene to P leistocene, 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
Sivapithecus
• 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)
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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
Ouranopithecus
Proconsul
africanus
Dendropithecus
macinnesi
Limnopithecus
legetet
Proconsul
nyanzae
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Ape Ancestors
Catarrhine Cladogram
Molecular Clock
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