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MSU ISS 210 - Ardipithecus and The Bipedal Revolution

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ISS 210 1st Edition Lecture 6 Outline of Last Lecture I. Louis and Mary LeakyII. “Virtual Anthropology”III. Taphonomists and DepositionIV. A Leopards PrayV. StratigraphyVI. Vulcanic TuffsVII. ChronometricsVIII. “Trapped-Charge” DatingIX. Species: Where do you draw the line?X. CatastrophismXI. UniformitarianismXII. Phyletic GradualismXIII. Punctuated EquilibriumXIV. Allopatric SpeciationXV. Homosapiens Sapiens XVI. Cladistics Vs. Evolutionary TreeXVII. The Disadvantages of BipedalismXVIII. Dentition and SkullsXIX. Tooth Enamel Wear PatternsOutline of Current LectureI. The Piltdown “fossil” II. Piltdown SkullIII. The Benefits to BipedalismIV. Bipedalism vs. knuckle walkingV. The case for bipedalismVI. Ardipithecus ramidusVII. Ardi’s AnatomyVIII. Ardi’s EnvironmentIX. Hominids in AfricaX. Map of ChadXI. Sahelanthropus Tchadensis or “Tourani”XII. The Human Evolution StoryXIII. Distinctive features: AustralopithsXIV. A. aferensis: Teeth and JawsXV. A. afarensis: “Lucy”XVI. Pelvis and Femur: Chimpanzee Australopitheorine and HumanXVII. Laetoli FootprintsXVIII. Laetoli Footprint: Thermal ImageXIX. How made stone tools?XX. A. garhi (2.5 mya) Bouri, EthiopiaXXI. Heavy Duty Scraper from Olduvai GorgeCurrent LectureI. The Piltdown “fossil” – Discovered in 1912, this skull with human and ape-like features provide the “missing link”– Someone hafted the jaw of an orangutan to a modern human cranium “fit” the model of the time– Discredited in 1953, it ruined career and reputationsII. Piltdown Skull– “Brain Bias” Theory-only a hominid with a large brain could walk bipedally– Brain evolved to make tools– Bipedalism evolved to carry tools – Impact– Discredited Dubois’s 1891 “Upright Ape-man”– Made acceptance of Dart’s 1924 “Southern apes” difficult – The 1974 discovery of a small brained, fully bipedal, 3.2 million year old A. afarensis (“Lucy”) ended the debate – Scientists began looking for older fossils and began finding them further westIII. The Benefits to Bipedalism– Look larger and don’t present a horizontal target to predators– See farther when in tall grass– Carry things about– Better able to cool the body and brain – Hairless and sweat glands– Aftord humans incomparable stamina and the ability to remain active in the sun for long periods and travel long distances easily. IV. Bipedalism vs. knuckle walking– “energy efficiency is determined by length of stride and amount of muscle activated in each stride– Humans use only 25% of the energy apes use whether knuckle-walking or walking uprightV. The case for bipedalism– Apart from a larger brain, upright bipedalism is the other uniquely human trait– Evidence of ancient “experiments” in bipedalism within a new ape niche, part arboreal, part terrestrial– Tattersal suggests earliest ancestor preferred upright posture and maintined it onthe ground– Early species (3-4 mya) pulled a seemingly random selection of possible dental, facial and cranial traits– Large hominid like or smale ape like ear openings – ForamenVI. Ardipithecus ramidus– Found at Aramis in Ethiopia in 1994 and proposed as the “root” of the hominid line – A bipedal chimpanzee with mix of ape and hominid features– Narrow molar teeth with thin enamel coating are ape like– Tiny chimpanzee like braincase has a forward shifted foramen magnum indicates it was– Habitually upright– Lived in densely wooded areaVII. Ardi’s Anatomy– Less muzzle and no dagger like canine teeth seen in chimpanzees– Opposable big toe but toes in the line to allow walking– Spine curved like humans; pelvis shorter and broader than apes – Flexible wrist that could bend backward – Suggests that ancestors never knuckle-walked forcing a rethink of what the last common ancestor walked like VIII. Ardi’s Environment– Savannahs had nothing to do with walking upright– Lived in a woodland area climbing fig and palm trees– Ate a woodland, not a grassland diet: fruits, nuts, tubers with insects, small mammals or bird eggs– Size, shape and distribution of enamel on teeth suggest a more omnivorous diet than chimpsIX. Hominids in Africa– Environment and Evolution– Plate tectonics raised the landscape of Eastern Africa creating the African rift valley from the Horn of Africa to Mozambique – Moisture from the Atlantic was trapped in the west maintaining tropical forest where apes evolved – The east was in the rain shadow and became dry with a mosaic of habitats in which hominids engaged– Recent discovers show that hominids emerged in the west as wellX. Map of Chad– Discovery of new fossils is a matter of looking in new places– Hominid fossils are no longer an “East SideStory” – Sanelanthropus tchadensisXI. Sahelanthropus Tchadensis or “Tourani”– 6 to 7 mya – A “mosaic” of chimpanzee and hominid features– If truly a hominid, then hominids branched off from chimps before 6 myaXII. The Human Evolution Story– Australopithecusmanesis (4.2 to 3.9 mya)– Found in Kenya in 1995 at Kanapoi and Allia Bay– Possessed wide, thick-enameled molars– Lived in riverine forest bordering on woodland and open areas– A. amanesis: upper and lower tibiaXIII. Distinctive features: Australopiths– Upright bipedal walkers but hardly “human” in other respects– Diet: grains, roots, tubers, and scavenged meat– Y5 cusped molars, reduced canine diastema and a parabolic dental arcade– Skull has chimp-sized brain case and a large strongly projecting face– Increased cranial capacity– Australopiths described as “bipedal apes”XIV. A. aferensis: Teeth and Jaws– Chewing teeth are big– Jaws are of primitive proportion– Enamel is thick as in later hominids– Canine teeth are smaller and more stoute-rooted than apes but larger and a bit more projecting than later humansXV. A. afarensis: “Lucy”– Broad pelvis and lower limb bones correlate with bipedal walking; “hyperadapted” to bipedalism – Longer arms with short upper arms, shorter legs, long curving hands and feet built for grasping, narrow shoulders and rib cage that widened dramatically– Bipedal. A slow runner but good at climbing favoring an environment with trees for shelterXVI. Pelvis and Femur: Chimpanzee Australopitheorine and Human– For chimps, walking on two feet is as energy efficient as knuckle walking– Human bipedalism is more efficient than chimp bipedalism– Indicates


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