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U of M ANTH 1001 - Lecture 19 11-21-17 The Gracile Hominins (29 pages)

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Lecture 19 11-21-17 The Gracile Hominins



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Lecture 19 11-21-17 The Gracile Hominins

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29
School:
University of Minnesota- Twin Cities
Course:
Anth 1001 - Human Evolution
Human Evolution Documents
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11 22 2017 Probable Hominins various Genera Gracile Hominins Australopithecus Robust Hominins Paranthropus P robustus P aethiopicus P boisei 1 Australopithecus anamensis southern ape from the lake Kanapoi Allia Bay Kenya East Africa 4 2 3 9 Ma 2 2 1 11 22 2017 Australopithecus anamensis Earliest biped with certainty Morphology Reduced canines Loss of CP3 homing complex thicker enamel than chimp thinner than later Australopiths strongly built tibia both knee ankle showing bipedality BUT long curved fingers 3 3 Chimpanzee Modern human Australopithecus anamensis Orrorin tugenensis 4 4 2 11 22 2017 Australopithecus afarensis southern ape from the Afar Afar depression Ethiopia also in Laetoli Tanzania and Turkana basin Kenya East Africa 3 9 2 9 Ma 5 5 The Hadar find AL 288 1 called Lucy an Australopithecus afarensis 6 3 11 22 2017 Cranial shape and brain size 7 Dental comparison of Chimp A afarensis Human 7 Intermediate canines U shaped dental arcade more like chimp Thick enamel like human even thicker Much larger molars than either 8 8 4 11 22 2017 Notice the chimp like intermembral index Comparison of Modern human and A afarensis Chimp A afarensis 9 Human valgus knee with bicondylar or carrying angle 10 5 11 22 2017 Broad femoro tibial knee joint Proximal Tibia Distal Femur Chimpanzee Lucy Modern Human Chimpanzee Lucy Modern Human 11 Figure 05 21d 12 6 11 22 2017 3 5 mya Mary Leakey at Laetoli Tanzania 13 Analysis of the Laetoli Footprints Russel Tuttle s comparison with Machigenga people of Peru a bipedal striding gait Analysis of cadence suggests a shorter stride than modern Note slightly abducted big toe relative to foot on the left 14 7 11 22 2017 Figure 05 23 15 Humerus Quadrupeds have more robust humeri than bipeds weight bearing Bicipital grove Deep very muscular Shallow limited upper body strength A afarensis bicipital groove is deeper than that of modern humans if not as deep as African great apes 16 8 11 22 2017 Thorax Shape and Scapula Placement Scapular Adaptations for Suspensory Locomotion Human Chimpanzee 18 9 11 22 2017 A afarensis fossil from Dikika Ethiopia 3 3 ma 3 year old 19 Alemseged et al 2006 Dikika 1 1 G gorilla H sapiens Chimp P trog 20 10 11 22 2017 Australopithecus afarensis Morphology arboreal Morphology general 375 500 c c large procumbent incisors prognathic face megadonty very large molars and premolars with thick enamel cranially oriented scapular glenoid curved phalanges long toes high intermembral index Morphology terrestrial anteriorly placed downward directed foramen magnum distinct foot arch distinct valgus knee angle 21 Chimpanzee 21 Modern human Australopithecus afarensis Australopithecus anamensis Orrorin tugenensis 22 22 11 11 22 2017 Topics Hypotheses for the origins of bipedality Last of the Gracile Australopiths Robust Australopiths Genus Paranthropus Dietary reconstructions of the Australopiths Australopiths Gracile genus Australopithecus Robust genus Paranthropus 23 Why bipedalism 1950s Bipedalism evolved to allow hunting of grassland game Now There is no evidence for hunting until much later in the Pliocene while bipedalism began in the Late Miocene 24 12 11 22 2017 Raymond Dart s Osteodontokeratic Industry 25 Hunter or Prey C K Brain s The Hunters or the Hunted A africanus 26 13 11 22 2017 The Savanna Hypothesis opening of the forest terrain into grasslands at the beginning of the Pliocene offered apes a new niche which then produced selection for more bipedalism 27 The Late Miocene Problem with the Savanna Hypothesis Woodland fauna like the kudu red colobus were associated with the earliest evidence for bipedal traits 28 14 11 22 2017 A Modified Savanna Hypothesis Problems Habitat reconstructions for individual sites can run foul of the Drunk under the Lamp Post Problem Forest habitats were decreasing due to climate change from mid Miocene Late Miocene apes were very diverse Selection for different ways to adapt to the new open landscape niche for being an ape This produced a mosaic pattern to the evolution of bipedal apes into the Pliocene generalist adaptation The Late Miocene record is so patchy that it is hard to identify which fossils are really on the hominin lineage until the Pliocene s A anamensis 29 Hypotheses currently seen as UNLIKELY to explain evolution of bipedalism 30 15 11 22 2017 UNLIKELY Bipedalism is good for vigilance against predators and threats IF SO why are baboons not now bipeds 31 Terrestrial feeding hypothesis UNLIKELY Gelada monkeys feed on grasses herbs while sitting in an orthograde position IF SO why are geladas not now bipeds 32 16 11 22 2017 Threat Display hypothesis UNLIKELY Being bipedal makes it easier to display Chimp males frequently display bipedally frequently quadrupedally as well This is a fairly temporary behavior to cause such large anatomical changes 33 Carrying Hypothesis UNLIKELY Provisioning monogamy BUT sexual dimorphism is HIGH when bipedalism begins 34 17 11 22 2017 Hypotheses currently seen as LIKELY to explain evolution of bipedalism 35 A Likely Carrying Hypothesis LIKELY Knuckle walking constrains chimp tool use 36 18 11 22 2017 Still Another Carrying Hypothesis LIKELY Open grassland is rich in food Remember central place foraging 37 The USO Hypothesis Underground Storage Organs tubers as Fallback Foods Thicker enamel and larger chewing surfaces of Australopithecus Paranthropus dentition compared to chimps gorillas Dental adaptations for USOs increase during Pliocene USOs developed in abundance with the end of the Miocene as seen by evolution of USO eating mole rats Correlation between mole rats and hominin sites suggests USO rich habitats occupied by hominins 38 19 11 22 2017 The Thermoregulatory Hypothesis Erect posture keeps you cool LIKELY 39 No Single Cause is Probable Multiple causal factors are more likely All successful hypotheses relate to the increase in distance between trees as climate got cooler and drier from the end of the Miocene through the Pliocene 40 20 11 22 2017 Chimpanzee Modern human Australopithecus afarensis Australopithecus anamensis Orrorin tugenensis 41 41 Unknown phylogenetic relationships due to poor preservation but probably an A afarensis Don t worry too much about K platyops Kenyanthropus platyops 3 5 mya 42 21 11 22 2017 Australopithecus africanus southern ape of Africa 3 5 2 0 Ma South African sites of Sterkfontein Makapansgat Taung 43 43 44 44 Australopithecus africanus Morphology 400 500 c c more globular cranium beginnings of a forehead Less

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