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Anthropoid Origins: Early Primates and their Evolution - Prof. P. L. Walker, Study notes of Theory of Evolution

An in-depth exploration of the early primates, specifically the adapids, omomyids, and the first anthropoids. It discusses their physical characteristics, adaptations, and differences from prosimians. The text also covers the environmental context of their existence and the evolution of the visual system and jaw structure.

Typology: Study notes

Pre 2010

Uploaded on 08/30/2009

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Download Anthropoid Origins: Early Primates and their Evolution - Prof. P. L. Walker and more Study notes Theory of Evolution in PDF only on Docsity! Anthropoid Origins 2SVRQQ CY] tase y Pee Ceciarecas rms : a a 3 j ' iy ' i > I I | Nae | 4 | ! - 1 | Mesopithens| | Propidheciss I poe | on | | an | So | ‘ | \ Larger 7 | Braincase ] | ~2/1/4)3 Dental I 2 Forme | | | = i | Anidluuet — Aegyetopithecia os . tia { a ‘ 4 r = \ \ } L_| | Room . \ J : “BB ' Larres ° a ‘ Rounded 3 Necrolemar 47 \ Brniease < ° j ee eae a . { : ‘ Betray a) AS — Frentiaoeg AY ( Phesaeslepans os Vertical | ria bo) é Lj Teronise ! | i ! | \ | I / ; ! I Nek tle Fane \ ie Beck aoa Down . a 5 Adapids • Notharctus and Smilodectes were typical members of the Adapidae • Their crania are similar to those of a modern lemur • Long hindlimbs suggest that they were vertical clingers and leapers Smilodectes Notharctus Differences between anthropoids and prosimians • Larger brain: The prosimian brain is smaller than that of most anthropoids of similar body size • Reduced emphasis on olfaction: Prosimians have large snouts with moist, dog-like noses and brains with large olfactory lobes. • Eyes move to the front for binocular vision • The post-orbital bar expands so that the back of the eye surrounded by bone • Fused mandibular symphysis: In adults, the jaw forms a rigid bony strut • Claws replaced by nails Eye-Socket Differences • In the anthropoids, the back of the eye socket is enclosed in a bony cup (postorbital closure). • In most prosimians the lateral border of the eye is protected by a strut of bone (postorbital bar) but there is no postorbital closure. • This difference reflects refinements in the visual system associated with with the anthropoid emphasis on sight Fusion of the sides of the jaw and skull • In prosimians, the joint between the two halves of the lower jaw in the area of the chin (mandibular symphysis) remains unfused in adults. • In anthropoids, the sides of the mandible fuses in adults so that the jaw forms a continuous strut of bone. • A similar difference is seen in the frontal bone. In most adult anthropoids the right and left frontal bones are fused at the midline; in prosimians they remain separate bones. The jaw of Eosimias Fayum Primates • Much of what we know about the early history of monkeys and apes comes from late Eocene and early Oligocene fossils discovered in the Fayum Depression about 60 kilometers south of Cairo, Egypt. • These remains document an adaptive radiation of squirrel monkey-sized (Oligopitehcus, Catopithecus) and marmoset- sized (Serapia, Arsinoea, Proteopithecus, Plesiopithecus) late Eocene anthropoids in North Africa. Catopithecus Fayum Primate Families • By the early Oligocene, the Fayum primate community was dominated by two anthropoid families: the Propliopithecidae and the Parapithecidae. • The parapithecids are smaller (marmoset sized) and more primitive than the propliopithecids. – They share traits such as the retention of three premolars with modern New World monkeys. – Other features of their legs and teeth were prosimian-like. • The propliopithecids were larger (4 to 6 kg) and had a number of advanced traits (such as two premolars instead of three) seen in modern Old World monkeys. Aegyptopithecus • A probable ancestor of the later apes as well as humans • Old World Monkey Dental Formula (2 premolars): 2 1 2 3/2 1 2 3 • Rear of eye socket closed, orbits convergent The Teeth of Aegyptopithecus • Lower molars have a five-cusp pattern that is very similar to later apes and humans • Rounded cusps suggest a fruit- eating adaptation The Brain of Aegyptopithecus • Organization of brain appears intermediate between that of prosimians and monkeys. • Snout indicates there was still an emphasis on olfaction The Origin of Apes and Monkeys PLATYRRHINI CATARRHIN (CERCOPITHECOIDS . HOMINOIDS _ “ f * LESSER APES GREAT APES : i QRANGUTAN GORILLA CHIMPANZEE | — " j \ } - SPIDER MONKEY ©” MACAQUE MILLIONS OF YEARS AGO ~ Miocene Primates • During the Miocene the Old World monkeys, apes and gibbons diverged • Early in the Miocene the apes had an adaptive radiation and moved into a variety of arboreal and terrestrial niches. • Toward the end of the Miocene the diversity of apes decreased while the diversity of monkeys increased Miocene Environments • During the Miocene there was an expansion of savannah-woodland environments in Africa and Eurasia • Tropical forests gave way to a mosaic of habitats including woodland savanna, true savanna, and semiarid regions. Miocene Apes • During the Miocene there was an adaptive radiation of Apes. At this time they were found in Eurasia and Africa • There were large, medium and small sized species of great apes as well as gibbon-like forms. • Most forms appear to have been quadrupedal rather than brachiators or knuckle walkers Gibbon-like Miocene Apes • A number of gibbon-like forms evolved during the Miocene • These include Oligopithecus Limnopithecus Pliopithecus OligopithecusPliopithecus Proconsul • Proconsul is the best known of these early Miocene apes. • This genus contained three species that ranged in size from a modern monkey to a modern chimpanzee. • The smallest, Proconsul africanus, had a narrow nose with a projecting chimpanzee-like face. • The brain of Proconsul was bigger than that of modern monkeys of comparable size. Fist-walking vs. Knuckle-waking Knuckle-walking • In the African apes, a ridge on distal end of the metacarpal resists hyperextension during knuckle-walking • This feature is not found in the fist- walking orangutan • The hand of Proconsul lacks any anatomical features associated with knuckle-walking Chimp Orang Gorilla The hand of Proconsul Dryopithecus • Apes such as Dryopithecus fontani were widely distributed in Eurasia and Africa during the middle Miocene to Late Miocene • Probably a forest-dwelling frugivores • Ranged in size from that of a large money to a chimpanzee • Probably involved in forelimb- dominated suspension Molar Shape • Ape molars tend to be rectangular • Hominid molars tend to be square Canine Size • Apes have long canines • Hominids have short canines Premolar Shape • Apes and monkeys have specialized “sectorial” lower first premolars • Humans lack sectorial premolars Ramapithecus • A late Miocene ape • Formerly thought to be the earliest hominid • Now considered to be a member of the of the genus Sivapithecus Sivapithecus • The ramapithecine Sivapithecus was once thought to be an early hominid. • New specimens, however, show that it is most likely an ancestor to the modern orangutan • These fossils date from about 8 m.y.a. and this suggests that humans and the African apes had separated from the orangutan linage by the Late Miocene Sivapithecus ChimpanzeeOrangutan Sivapithecus Early Australopithecines • Ardipithecus ramidus • Australopithecus anamensis • Australopithecus afarensis • Australopithecus garhi
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