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ANTH-UA 2 Chapter Notes -Treeshrew, Marsupial, Mesozoic

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Richard Bailey

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Origin of Primates
The Mesozoic and Beyond
Dawn of the Age of Mammals
Mammals that first appeared during the late Triassic Period most closely resembled the
living monotremes
Jurassic Period - first marsupial and placental mammals appeared
Cretaceous Period - diversification of marsupials and eutherians
Diversification of angiosperms at the end of the Mesozoic probably caused the
diversification of mammals in the middle to late Cretaceous
Led to pollination of flowering plants by insects
Abundant insects probably attracted vertebrates
The K-T Boundary
At the end of the Mesozoic, drastic environmental changes (probably arising from an
asteroid or comet crashing into the surface of the earth) caused or contributed to the
extinction of the dinosaurs and generated opportunities for mammals.
K-T Boundary - the end of the Cretaceous Period and the beginning of the Tertiary
period; marked by the aforementioned wide-scale faunal changes
Evidence for asteroid theory comes from a giant crater called Chicxulub in the Yucatan
Asteroid probably caused firestorm followed by global cooling would have
killed off terrestrial plants herbivorous dinosaurs would die out carnivorous ⇒ ⇒
dinosaurs would starve to death
New environment (absence of large prey animals) favored small, insect-eating mammals
over dinosaurs
Replacement of mammals at the K-T boundary
Temperatures were warmer and differed less between the equator and the North and
South poles during the Paleocene and early Eocene, so the first primates existed fairly
far north and south
Changes in the Paleocene: the Origin of Primates
Paleocene Epoch produced many archaic groups of mammals that are not precisely like
any living group
Plesiadapiforms = mammalian order or suborder that may be ancestral to later
Primates, characterized by some but not all of the primate trends
Controversy as to whether or not they are true primates; suggested that they are
more closely related to other mammals (tree shrews, colugos, or bats)
New fossil evidence indicates that at least some plesiadapiforms were true
primates that diverged before the last common ancestor of living species
Paleontologists classify fossils by looking at teeth and bones; must follow primate trends
to be classified as primates
Problems with plesiadapiforms:
Prognathic face = projection of the face well in front of the brain case
Lacked postorbital bar = a bony ring encircling the lateral side of the eye but not
forming a complete cup around the eye globe
Many possessed rodent-like lower incisors that were separated from the
premolars by a large diastema (gap between the anterior teeth)
Some had claws and lacked an opposable big toe
Purgatorius - earliest representative of the plesiadapiforms (only found jaws and teeth)
Less specialized teeth, more generalized dental formula
Plesiadapiform radiation shows that very early primates were anatomically more
primitive than living primates in almost all respects
Important early adaptation was the evolution of hand proportions suitable for grasping
fine branches
Why Primates?
Paleocene flowering plants caused an increase in insects primate ancestors took
advantage of these changing resources by eating insects and possibly fruit from new
Emphasis on vision over olfaction and tactile pads on fingers were more likely for
catching insects than survival in trees (visual predation hypothesis)
Early Primates of the Eocene
Climate warming at the beginning of the Eocene resulted in the replacement of archaic
Paleocene mammals by the first representatives of modern orders of mammals
Fossil record of the Eocene reveals the first true primates
Strepsirhine-haplorhine split occurred during the Eocene
Grande Coupure (“big cut”) - large-scale extinction and replacement of species at the
Eocene/Oligocene boundary (due to drop in global temperature)
Two superfamilies: Adapoidea and Omomyoidea
Eocene fossils are true primates because:
Slightly larger brains than plesiadapiforms
Eye sockets positioned on the front of the face
Complete postorbital bar
Opposable big toe
Nails on fingers and toes
Reduction of snout and whiskers (smell less important)
Adapoids (Strepsirhine Ancestors)
Adapoids = mostly small- to medium-sized primate ancestors; slow-moving arboreal
quadrupeds that were diurnal and ate fruits and leaves
3 families: Notharctidae, Adapidae, and Sivaladapidae
Resemble modern strepsirhines in primitive ways; lack features of modern strepsirhines
(ex: tooth comb)
Considered the most primitive group of early modern primates known
Adapoids probably gave rise to strepsirhines before the evolutionary divergence of
lemurs and lorises (evidence for strepsirhine-haplorhine division instead of anthropoid-
loris division)
Omomyoids (Haplorhine Ancestors)
Omomyoids = smaller-bodied primate ancestors that ate diets of insects and fruits and
had larger orbits, probably for a nocturnal lifestyle; probably arboreal quadrupedalism
and leaping (like mouse lemurs and galagos)
Omomyoids differ from tarsiers: eye sockets are not as large, ankles do not possess
features for exceptional linking
Regarded as Eocene primates that had recently diverged from adapoids and may have
given rise to the common ancestor of both tarsiers and anthropoids
Continental Drift and Eocene Primates
Europe and North America were joined by a land bridge, and there was little difference in
Primates could have freely walked between the two explains Eocene primate
Selective Pressures Favoring the Strepsirhine-Haplorhine Split
Anatomical clues suggest that adapoids and omomyoids divided up the available food
resources avoid competition
Adapoids ate leaves and relied on smell gave rise to strepsirrhines
Omomyoids focused on fruit and insects gave rise to haplorhines
Evolution of Higher Primates
Representatives first appeared in the late Eocene and early Oligocene epochs
Earliest higher primates are generalized monkeys that probably gave rise to all later
higher primates
The First Monkeys?
Grande Coupure created challenges and opportunities for animal populations alive at the
Adapoids and omomyoids nearly vanished from North America and Eurasia
Monkeys first appeared in the Oligocene
Higher primate anatomical features - greater enclosure of orbits, smaller snouts, fewer
teeth, fused frontal bone, fused mandible, larger body size
Two windows for the origin of anthropoids: Eocene of (1) China, (2) North Africa and the
Middle East
Relationships between early Asian and African forms are hotly contested
Fayum depression in Egypt - during Eocene and Oligocene, was a lushly forested area
surrounding a large river system that supported a great diversity of tropical fauna and
flora; three families: