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Lecture 15

Lecture 15 - Hominin Origins - January 29.docx

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University of Toronto St. George
Keriann Mc Googan

January 29, 2013. Lecture 15 – Hominin Origins Quiz 2: March 5h  In class, 1 hour long  Chapters 8-14  Lectures Jan 8 – Feb 26 (inclusive)  Format o Multiple choice o Fill-in-the-blank o Short Answer  Study guide will be posted Hominin Origins in Africa  The bipedal adaptation o Scenarios o Anatomy  Early hominin fossils o When? o Where?  Blah blah  Blah The Bipedal Adaptation  Knowledge of bipedal anatomy can help us determine where/when it developed  Bipedal “problem” o Maintain balance, need a stable centre of balance to maintain upright position while weight shifts from leg to leg during walking o Abductor muscles allow our pelvis to remain upright while walking, torque pulls at muscles instead of pelvis which would twist it down and to the side of the unplanted leg  1. The Pelvis o Ossa coxae  Hip-bones extend out and to the side and are more rounded whereas great ape hip bones are thinner, more angular, and extend upwards  Allows for difference in the angle in which weight is dispersed through the pelvis o Basin-like shape  To house abdominal organs and muscles o Muscle attachments  Gluteus maximus is farther back, behind our hips, than in apes where theirs is more to the side  Helps pull our legs up and behind us instead of out and to the side like in great apes  Also hamstrings attached more to our fibula  2. The Foramen Magnum o Hole at the base of the skull where the spinal cord attaches o In humans, farther underneath the skull, farther to the back of the skull in chimps o Helps for keeping the skull upright at the top of the body, balanced the skull o Spinal cord enters the skull vertically through this change instead of more horizontally/diagonally like in great apes  3. The Spine o Very s-shaped design to it in humans o Two distinctive curves in the spine allows for weight to be centered around the pelvis o More bow-shaped in chimps  4. The Lower Limb o Lengthening of hind limb to allow for larger strides when walking o Bones in humans changed to angle inwards rather than curving outwards like in great apes o Femur angled inwards allows for keeping the lower limbs directly under the body instead of out to the side  5. The Foot o Big toe in humans is enlarged and brought in line with other toes o Longitudinal arches in our feet to help absorb shocks and allows for more spring  Explains issues in walking for flat-footed people Early Hominins and Bipedalism  Habitual Bipedalism: bipedalism as form of locomotion exhibited MOST of the time  Obligate Bipedalism: bipedalism is the ONLY form of hominin terrestrial locomotion  To what degree did our human ancestors use bipedal locomotion?  Anatomical changes for bipedalism 4MYA  Obligate bipeds? o Sterkfontein South Africa: divergent big toe (not in line with other toes)  Found fossil evidence of early hominin foot structure  Showed arch in foot structure, but still had divergent big toes o East Africa: flexible ankle (indicates continued adaptation to climbing)  BUT most early hominins were both habitual and obligate bipeds Early Hominin Fossil Locales  East Africa is where a lot of fossil evidence has been found o Rift exposed river bed? o Olduvai Gorge among this area  South Africa also had a couple important finds  99% of all finds came from Eastern or Southern areas Cranial Capacity  Absolute measure of brain size or volume  Cubic centimeters (cc) Early Hominins  3 groups  1. Pre-Australopiths 7-4.4MYA o Sahelanthropus tchadensis  Found in Chad  6-7MYA  Mixture of traits  Found a nearly complete cranium as well as fragments of jaw and teeth  Oldest fossil find, also one of the most complete  Was found outside of the condensed Eastern Africa rift  Showed us that the early hominins occupied a much larger geographic space than previously thought  Mixture of some primitive and derived hominin traits  Derived traits:  Small canines  Relatively flat or small face  Enamel thickness is intermediate  More anterior foramen magnum (towards the front) o Might have used bipedal locomotion to some extent  Primitive traits:  Brow ridge bigger than gorilla o Sagittal crest  Small chimp-sized cranial capacity (320-380cc)  More features in common with hominin line than with great apes  Probably was bipedal, but unsure if they practices habitual bipedalism or were just capable of it  Post-cranial structure indicates they might have mostly used quadrupedalism  Thicker enamel is very Miocene  Debate between classifying it as first hominin or last common ancestor between hominins and apes o Orrorin tugenensis  Found in Central Kenya  Found fractures of leg, teeth, arm, finger  6MYA  Misture of ape-like and human-like features  Limb bones may suggest bipedalism  Earliest definitive hominin  Molars are human like, premolars, canines and incisors more chimp
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