ASB 194 lect12.doc


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HUMAN ORIGINS- AN EVOLUTIONARY HISTORY I. Primates have their origins at the end of the Cretaceous period, which ended about 65 million years ago (mya). At the end of this period occurred the great dinosaur extinctions, the emergence of flowering and fruiting plants, and the beginning of the "age of mammals," in which there was a tremendous expansion in the diversity of species of mammals. This event seems related to the impact of the Chicxulub asteroid which released 100 million megatons of explosive power and probably decimated much of life on earth. A) most or all of primate evolution occurs in the CENOZOIC ERA of geological time following the cretaceous, The Cenozoic is divided into two periods: 1) the QUATERNARY period 1.9-present 2) the TERTIARY period 65-1.9 MY ago These two PERIODS are divided into the following EPOCHS SUMMARY OF PRIMATE EVOLUTION EPOCH M YA CLIMATIC REGIME PRIMATE EVOLUTION PLEISTOCENE 2 Cooling, periodic Homo sapiens glaciations, rather Homo erectus rapid climate fluctuations Homo habilis PLIOCENE 5 Increasingly cooler, dryer Hominins: Australopithecines Expansion of savannah habitat MIOCENE 23 Cooling "ground apes:" Dryopithecus, Forest habitat expands, then contracts Ramapithecus, Sivapithecus OLIGOCENE 36 Cooling, drying First Anthropoids Reduction of tropical forests, EOCENE 54 Warming trend, less seasonal Prosimians PALEOCENE 65 Mammalian radiation, warm and wet Rodents/primates into trees II. Primate evolution during the Tertiary period was closely tied to global climate changes , specifically periods of warmer, wetter global climates alternating with cooling and drying. These long term climate changes caused the alternate expansion and shrinking of the primary primate habitat: tropical rainforests.
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Early primates looked much like lemurs and tarsiers. Some were nocturnal and probably ate insects. Other were probably diurnal and ate plant material. A) During cooling and drying periods from Eocene to Oligocen e rain forest habitats were reduced, and some ancestral primate species adapted themselves to temperate forests. The Anthropoids , ancestors of modern monkeys and apes, first appear in the fossil record around 35 million years ago . The fossil monkeys (eg Aegyptopithecus) from this time are very small. Dental patterns show that Old World and New World monkeys diverged very early during this period. How did New World monkeys get to South America from Africa 50 mya when the continents were separated by 2,000 miles of open ocean? Best guesses suggest they rafted on floating vegetation (as did the rodents). B) During the miocene the climate gets much cooler and dryer . But the first Hominoids (Apes) appeared about 27 million years ago and lived in rain forest environments. Hominoids have no tails and a few other subtle anatomical differences from the monkeys. They (eg. Proconsul sp.) ranged in size from 20 to 80 pounds, walked like modern quadrepedal monkeys, and probably ate ripe fruit. As the miocene became drier the Hominoids radiated into new niches and were
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This note was uploaded on 03/01/2011 for the course ASB 194 taught by Professor Hill during the Spring '11 term at ASU.

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