Chapter Study Outline
1. Why Did Primates Emerge?
a. Theories of primate evolution
i. Arboreal hypothesis
(1) Smith and Jones
(2) Primate traits such as grasping hands and binocular vision were adaptations to life in the trees.
(3) Moving from the ground to the trees caused selective pressures that resulted in the ancestral primate.
ii. Visual predation hypothesis
(1) Challenges arboreal notion: many mammals are arboreal without having evolved primate traits.
(2) Matt Cartmill proposed that primate traits evolved in response to preying on insects and other small creatures.
(3) The exploitation of small prey resulted in the primate suite of adaptations.
(4) However, this visual predation hypothesis does not explain fruit-eating primates.
iii. Angiosperm radiation hypothesis
(1) Randall Sussman proposed that primate traits were a response to the development of fruit-bearing angiosperm plants.
2. The First True Primate: Visual, Tree-Dwelling, Agile, Smart
a. Primates in the Paleocene?
i. Paleocene fossils a possible candidate for the early primate ancestor
(1) Found in western North America, western Europe, Asia, and possibly Africa
(2) Lack postorbital bar and other primate traits
(3) Possibly a separate order, but still potentially related to primates
b. Eocene Euprimates: The First True Primates
i. First true primates (euprimates) in Eocene epoch, as early as 55 mya
ii. Clear primate traits, including postorbital bar, large brain relative to body size
iii. Adapids and omomyids
(3) Widely diverse species, most with small body size
(4) May have evolved from proprimates in Paleocene
(5) Evolution occurred in period of global warming
3. Evolution of the Euprimates
a. The Anthropoid Ancestor: Euprimate Contenders
i. There is debate among scientists as to the ancestors of living primates.
ii. One possibility is an Eocene primate called a basal anthropoid.
(1) Fossils were found in Asia and Africa.
(2) Some scientists regard these forms as the first true primates, though of exactly which genus is debated.
b. Basal Anthropoids
i. The Oligocene was a period of global cooling and widespread plant and animal extinctions.
ii. Most primate fossils from this period come from the Fayum region of Egypt.
iii. Fossils from this time period include prosimian fossils as well as those of three groups of higher primates.
4. Early Anthropoids Evolve and Thrive
a. The origins of catarrhines are clear: Aegyptopithecus. The origins of the platyrrhines are less clear. The first South American primate is Branisella, from Boliva, dating to 26 mya.
5. Coming to America: Origin of New World Higher Primates
a. Four competing hypotheses attempt to explain how anthropoids got to South America.
b. Fossil evidence is good for some hypotheses but not for others.
c. Some evidence suggests platyrrhines evolved in Africa, then migrated to South America.
6. Apes Begin in Africa and Dominate the Miocene Primate World
a. The Miocene deposits in Africa provide evidence for a group of primates called proconsulids, which date to 22–17 mya.
b. A diverse number of taxa, with 10 genera and 15 species.
c. Proconsul is the best known of these genera.
d. Skulls and teeth are apelike in appearance; rest of skeleton is monkeylike.
7. Apes Leave Africa: On to New Habitats and New Adaptations
a. The fossil record suggests apes evolved in Africa and spread to Europe and Asia.
b. Apes in Europe: The Dryopithecids
i. Larger than earlier apes
ii. Resembled living apes in many traits
c. Apes in Asia: The Sivapithecids
i. Sivapithecus is thought to be ancestral to orangutans due to skull similarities.
ii. Even more similar to orangutans is the newly found Khoratpithecus.
iii. Also related is the ape Giagantopithecus, which is dated to 8–.5 mya and is thought to have stood nearly 3 m (9.8 ft) tall.
d. Dead End in Ape Evolution: The Oreopithecids
i. Another branch of apes, orepithecids, are believed to be an evolutionary dead end.
e. Climate Shifts and Habitat Changes
i. Climate changes occurred during this time in Europe, Aftica, and Asia, resulting in the disappearance of fruit resources commonly exploited by the apes.
f. Miocene Ape Survivors Give Rise to Modern Apes
i. A few survivors of this event evolved into modern apes.
8. Apes Return to Africa?
a. The fossil record for the late Miocene is too fragmentary to shed light on the question of whether early hominids descended from Miocene ancestry in Europe or Africa.
9. Monkeys on the Move
a. As the apes evolved, so did the monkeys in the Old World and the New World expanded and radiated.
b. Fossils with cercopithecoid traits first appear in early Miocene.
c. The radiation of monkeys continued into the Pliocene and Pleistocene, then declined as habitats and climates changed, or perhaps even due to human hunting.