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- Lab 6 Notes Fall 1997 Australopithecines Post-Cranial Adaptations to Bipedalism Kevin L. Callahan Lab 6 Purpose of the lab To examine what features Australopithecines had that are "in between" apes and humans, which traits are closer to humans, and which are closer to apes, and which traits are unique. What is an Australopithecine? "Australopithecines" are for purposes of this class composed of Ardipithecus ramidus, the Australopithecines and the Paranthropines. Australopithecines are hominids and habitually bipedal. Australopithecines are chimp-like in their brain size and human-like in their bipedalism. Quiz next week on this lab There will be a quiz next week on this lab. Be prepared to identify two features related to positional repertoire (e.g. bipedalism) for different major bones and body parts. Remember that the Written Assignment is due on Tuesday in lecture next week. Midterms and quizzes will be handed back at the end of this lab. Australopithecine Positional Repertoire You will make detailed observations of comparative anatomy between three species. Australopithecines are the earliest known bipedal primates. Paranthropines are more generally more robust (larger) than Australopithecines who are gracile (smaller). Australopithecines are all African Most fossils are found along the East African Rift Valley or in the Transvaal region of South Africa. You will be comparing the Australopithecines to to the human and the chimp. Is the feature more like the human or the chimp. This will vary from one feature to the next. Terms you need to know for this lab foramen magnum - the "big hole" which is where the spinal cord enters the cranium. On the bipeds it is centered and the cranium balances over the spine. humero-femoral index - another version of the intermembral index or which is longer the arms or the legs. Upper arm and shoulder Terms proximal humerus - the upper arm near the shoulder. greater tubercle - where the pectoral muscle attaches to your upper arm. The size indicates pectoral development. The pectoralis major is the "pecs" that run across your upper chest. bicipital groove - a "V" shaped notch that is on the humerus which indicates bicep development Upper arm terms biceps - the muscle that contracts your forearmarm. You use it to do a chinup. The biceps originate on the scapula (shoulder blade and one strand runs down thie tube callled the bicipital groove. Apes have much stronger muscles for climbing that humans do so their greater tubercle and the bicipital groove are much more developed than humans. Distal (distant) humerus and "elbow" Terms Trochlear notch - the hook on the elbow on the ulna (under) shaped like a big "C." Chimps have a wider trochlear notch because they spend more time moving quadrupedally. A wider notch helps with weight bearing. Would you expect this to be more like ours or a chimps in an Australopithecine. "Elbow" Terms olecranon fossa - a fossa or "depression" at the distal (distant) end of the humerus (upper arm) that in apes is deep and in humans is shallow. It stabilizes the elbow for knucklewalking or hanging in an ape. Our elbow is less stable which may enhance carrying and tool use. Hands metacarpals - bones in the palm phalanges - fingers Humans have shorter and straighter fingers and palms than apes because we rarely hang from branches and we manipulate objects more. apical tufts - the ends of our fingers are broader than apes to give humans very sensitive finger tips and to enhance manipulation of objects. The Shoulder Blades glenoid fossa - The depression in the shoulder blade that articulates (attaches to the humerus (upper arm) to make your shoulder joint. In chimps, who hang a lot, the shoulder points more towards the cranium or head and this allows the center of gravity to be more centered. See the diagram on page 9. The Pelvis The ilium of the pelvis is bowl shaped on a bipedal human and flat and long on a chimp which uses many forms of locomotion. What would you expect the Australopithicine to be like? The station has an Efe (or "pygmy"I.e. a modern human) ilium which is about the size of the Australopithecine pelvis for doing the comparison. The Pelvis The pelvis is made up of 2 inominates - the ilium and ischium and a pubic bone. Humans walk a lot so they have a larger gluteus maximus (buttocks) than chimps do. A short broad illim provides greater area for muscle attachmentss. Thicker ilia also withstand more force. The pelvis must also allow for the head of the child to pass through during childbirth. Note: Stations 4 and 5 are the same Stations 4 and 5 are the same material since we have 2 copies of the Australopithecine inominate. You only need to visit one of them during the lab. There are 7 lab stations total. Pubic bones the pubic bones are in the front of the pelvis and where they come together to the point they join the rest of the pelvis is the "length of the pubic bone." The Australopithecine pubic bone is longer than in a humans (adjusted to the same body size). Look at Fig. 18 on Page 13. The Hip the acetabulum - is the depression in the pelvis that the femur (upper leg bone ) articulates or attaches to. femu- is the large upper leg bone and the head of the femur is thick in humans who walk upright all the time. the bicondylar angle - is the angle that the femur has that allows our knees to be under our center of gravity for walking. The Knee In humans the leg angles in from the hip to the knee. In apes, the weight passes straight down giving them a waddle. See p. 16 of your lab handout. The condyles - the round ends of the femur can be placed on a table and the angle of the femur to the knee can be reconstructed for chimps, Australopithecines, and humans. Knee terms Condyle - just means the knobbed end of any bone. The condyle articulates or fits into the "fossa" or groove or opening in another bone. The Foot The human foot is specialized for habitual bipedalism. Our talus (or anklebone) is "robust" (large and strong) and is horizontal for the tibia (lower leg) to articulate with. Humans have an inline big toe (hallux) which is good for bipedalism but not for grasping. The Foot Chimps use their feet for climbing and also terrestrial locomotion and their heel bone (calcaneous) is smaller than ours. Human feet have an arch (like a shock absorbing spring). Australopithicines Australopithecines were probably fairly efficiently bipedally and are in between apes and us but they were more like us. Look at the Laetoli footprints cast. Mary Leakey et al. found these Australopithecine footprints in Tanzania. The cast is cracked and is going back to the manufacturer so don’t touch it. Australopithecines Australopithecines also probably could easily climb trees to find food and sleep at night and were probably better climbers. They combined terrestrial bipedalism with arboreal suspensory positions or climbing. Early Australopithecines had brains about the size of a chimps (400 cc’s or the volume of a Pepsi can). Our volume is about 1200 cc’s or the size of three cans. Bipedalism evolved first Bipedalism evolved before the increase in brain size. Traits evolve at different times and rates.
Lab 1 Notes Fall 1997
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