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Lecture 3

AN 102 Lecture 3: PART III - OUR ORIGINS

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Quinnipiac University
AN 102

PART III – OUR ORIGINS LIFE BEFORE THE PRIMATES The Origin of Life • The history of the earth is divided into four eons, which are further broken down into eras, which are still further broken down into periods… • Precambrian – a term that is used informally to refer to earth’s history before the Cambrian period of the Paleozoic Era • Precambrian time includes the Hadean, Archean, and Protezoic eons The Paleozoic era – (542 – 251 mya) • Cambrian period... • Rapid diversification of many complex multi-celled organisms • Origin of the first vertebrates—the primitive jawless fish • Some of these early invertebrates adapted to living partially on land—the first primitive amphibians • The fossil vertebrate Tiktaalik documents the transition from early fish to tetrapods (vertebrates with limbs) • Later on in the Paleozoic era, complete adaption to living on land occurred in the first primitive reptiles • Mammals and birds eventually evolved from reptiles • Split into two major evolutionary lines: 1.) Modern-day reptiles and, 2.) Therapsids (mammal-like reptiles) • Represent the beginning of transition that eventually led to later mammals • Underwent adaptive radiation in the Permian period of the Paleozoic era • Dental adaptions made the therapsids well-suited to life on land, allowing them to forage and hunt The Mesozoic era – (251 –65.5 mya) when the dinosaurs were dominant and when mammals and birds appeared • As dinosaurs became more dominant, the therapsids declined and eventually became extinct; however, before they died out, some therapsids evolved to become the first true mammals… • During the Triassic period, the monotremes (egg-laying mammals) evolved • The first placental mammals evolved during the Jurassic period ▪ Bird-like reptiles also evolved during this time • The end of the Cretaceous period is marked by the mass extinction of dinosaurs and many other organisms ▪ Most common hypothesis: an asteroid or comet hit the earth with tremendous force, kicking up vast clouds of dust and blocking the sun • Temperatures dropped, and many plant forms became extinct; as plants died, so did the plant eaters and those who ate the plant eaters… • Considerable geologic evidence The Cenozoic era – (65.5 mya – present) when primate and human evolution occurs • Epochs – a subdivision of a geologic period • Continental drift – the movement of continental land masses on top of a partially molten layer of the earth’s mantle that has altered the relative location of the continents over time Paleocene epoch – (65.5 – 55.8) the primate-like mammals appeared • Small, quadrupedal mammals whose arms and legs were well adapted for climbing • Considerable diversity—variation in body size and dental specializations • Lack a postorbital bar ▪ Carpolestes simpsoni – (56 – 55 mya) a species of primate-like mammal that had some derived primitive traits; intermediate between primate-like mammals and true primates • Small, arboreal fruit eater • Lacked certain primitive traits o No stereoscopic vision • Foot adapted for grasping and an opposable big toe, as well as a nail rather than a claw on its big toe Eocene epoch – (56 -34 mya) the first true primates, primitive prosmians, appeared • Climate was warm and humid • Land environment was tropical and subtropical ▪ Initially, the continents of Europe and North America were still joined, resulting in the migration and similarity among the fossils we find in that specific region • Aquatic mammals first appeared, along with other modern-day mammals • Adaptive radiation of the first true primates—the early prosimians… ▪ The Eocene forms possessed stereoscopic vision, grasping hands, etc. ▪ Snout is reduced and teeth are closer together ▪ Possessed a postorbital bar and had larger brain cases ▪ The large size of eyes of some Eocene primates suggests that they were still nocturnal • Similar to living prosimians • Two groups: 1.) Primary diurnal leaf and fruit eaters, which is broadly similar to modern lemurs and lorises, and 2.) Smaller nocturnal fruit and insect eaters, which is broadly similar to modern tarsiers • Many different species ultimately became extinct; others evolved Ito present-day prosimians Oligocene epoch – (34 –23 mya) anthropoids underwent an adaptive radiation • Climate cooled during this time • Expansion of grasslands and a reduction in forests ▪ Change in climate resulted in southward movement of primate populations • Oligocene anthropoids show continued reduction of the snout and nasal area, indicating a greater reliance on vision than on smell • Fully enclosed eye socket • Smaller eye orbits suggest that they may have been diurnal • Small and arboreal • Generalized quadrupeds • Diet appears to have consisted of fruit supplemented with insects and leaves • How did NWM get to the New World? • One explanation: Anthropoids reached South America by “rafting” ▪ Small populations of monkeys could have survived long enough on these floating islands to complete a trans-Atlantic trip Miocene epoch – (23 – 5.3 mya) several adaptive radiations of hominoids occurred; the oldest known possible hominins appeared during the Late Miocene • Roughly half of all modern mammals were present during this time • South America and Australia were isolated due to continental drift • Eurasia (Europe and Asia) and Africa joined during part of the Miocene • Postcranial – the part of the skeleton below the skull • Proconsul – (21 – 14 mya) a genus of fossil hominoid that lived in Africa and that shows a number of monkey characteristics • Considerable variation, particularly in overall size • The skeletal structure shows a mixture of monkey and ape features • Did not have a tail • Limb proportions are more like that of a monkey than an ape; limbs roughly the same size ▪ Arms and hands are monkey-like; shoulders and elbows are more ape-like • Un
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