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Study Questions Exam III - Lauren Salzman Unit 3 Study...

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Lauren Salzman Unit 3 Study Questions Lecture 9a. Hominid evolution 1. Where and when did the earliest hominoid-hominid ancestors evolve? The earliest hominoid-hominid ancestors were Sahlenthropus tchadensis which were found in Chad, Central Africa between 7 and 6 million years old, Orrorin tugenesis which lived in East Africa about 6 million years ago, and the Ardipithecus ramidus which lived in East Africa about 5.8 to 4.4 million years ago. This evidence suggests that the beginning of hominid evolution were spread throughout East and North Africa. 2. What is Sahelanthropus tchadensis ? Where was it found? When did it live? What are the traits which suggest that Sahelanthropus tchadensis may have been an ancestor of hominids. Sahelanthropus tchadensis was found in Chad, Central Africa near the southern Sahara desert. It evolved between 7 and 6 million years ago. This fossil had some advanced hominid features. Its face is more vertical than apes, and the orbits are separated by a very wide interorbital pillar and crowned with a large, thick, and continuous raised thick brow ridge. The teeth are also smaller and within the range of early hominids. 3. What is the defining characteristic of hominids? The defining characteristic of hominids is bipedalism. 4. What evidence suggests that the australopithecines were erect bipeds? Australopithecines are considered hominids because they are characterized by the reduced size of canines and bipedal locomotion. They have uniquely associated hominid traits. What differs them from apes are the previously mentioned traits along with an anterior placed foramen magnum and the bicondular angle. Dietary adaptations are within their teeth; gracile can eat softer foods, such as ripe fruits. Robust can eat coarse vegetation, foods that are hard to chew (nuts, seeds, etc) 5. List two features of the post-cranial skeleton that reflect bipedal locomotion. Two features of the post-cranial skeleton that reflect bipedal locomotion that the lower limb bones are thick with a big trochanter and a broad pelvis shape. 6. What is the cranial & postcranial (from the neck down) evidence suggesting that australopithecines were hominids & not hominoids?
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The foramen magnum is located to the middle to base of the skull, as in modern humans, indicating that the australopithecines maintained an erect posture. Also, the anatomy of the pelvis and the placement of the femoral neck with the relationship to the pelvis indicate that the australopithecines had a mode of bipedal locomotion. The most dramatic confirmation that the australopithecines walked bipedally is found in the “footprints” discovered in 1978 at Laetoli in Tanzania. 7. What are the two major Australopithecine groups? What are the main differences between these two groups of Australopithecines? (consider tooth size, muscle size, diet, etc.) The two major australopithecine groups are robust and gracile. The main differences between these groups were that the robust australopithecine had larger and less generalized dentition along with bigger/flatter molars.
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