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Skeletal Features of Bipedalism Professor Janaki Natalie Parikh

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1 Skeletal Features of Bipedalism Professor Janaki Natalie Parikh

2 Bipedalism and the Hominid Family Criteria for membership in Hominid (Human) family: bipedalism Larger brains did not come first, in fact, increase in cranial capacity happens millions of yrs. Later Following are skeletal features that allow for &/or indicate bipedal locomotion 1. placement of the foramen magnum (?)

3 Skeletal Features of Bipedalism Foramen magnum: Latin, “large hole”, cranial opening where spinal column articulates placement indicates type of locomotion 2. S-curvature of the spine: not present at birth, we normally settle into an S-curve due to pressure exerted on the spine from bipedality, also narrow rib cage, signif. Diffcs in the lumbar region

4 Skeletal Features cont’d Fossil vertebrae wouldn’t be intact, how do we know what curvature existed? Soft tissue always leaves an impression upon bone! 3. Bipedal pelvis (?) component bones: Illium (pelvic blade) Ischium Pubis

5 Bipedal pelvis cont’d C himp’s illium: long, narrow & flat Biped’s (opposite): short, broad (wide) & curved Results: lower center of gravity, better stability and support for weight of internal organs 4. Femur: bicondylar angle (femoral angle): purposefully knock-kneed. Keeps our feet planted w/in our center of gravity, also, helps distribute upper body weight

6 Bipedal feet 5. Bipedal feet: foot arches. Purpose? Strong, supportive structure, absorbs impact 6. Non-divergent big toe, a chimp’s big toe is fully divergent. Their toe is adapted for grasping, ours is adapted for balance & support ml ml Now, back to geologic time pwrpt)

7 Robust vs. Gracile Grade Hominids Robust Large jaws (buttressed mandible) Molarized premolars & lrg molars (grinding teeth) Gracile Smaller jaws, no buttressed mandible Smaller back teeth

8 Robust vs. Gracile Grade Hominids Robust Jaws muscles anchored on top (sagittal crest) Gracile Jaw muscles anchored on the side (no sag. Crest)

9 Robust vs. Gracile Grade Hominids Robust Flaring zygomatic arches Cranial capacity? Smaller cranial capacity Gracile No flaring zygom. Arches Larger cranial capacity

10 Robust vs. Gracile Grades What can attribute these diffcs to? The key is diet! These are not taxonomic designations, but rather adaptations to a specific diet Robust: ate a diet rich in hard foods that graciles didn’t have the dentition to process Which of these grades is ancestral to modern humans? Gracile. The robust species eventually died out.

11 Comparisons of cranial capacity Chimpanzee:394 c.c. (mean) Gorilla:506 c.c. (”) How about anatomically modern humans? (A.M.H.) A.M.H.:1325 c.c.!!! (encephalization) Earliest hominids by comparison? All results below 500 c.c.’s. Increase in brain sz. did not come 1 st !

12 Australopithecus anamensis 4.2-3.8 m.y.a., E. Africa (N. Kenya), gracile Older than Lucy’s species Strong evidence of bipedality Thick molar enamel, dentition still ape-like

13 Australopithecus afarensis 4-3 m.y.a., E. Africa, gracile Features: Mixture of human & ape like traits face: prognathic like a chimp Teeth: CP3 complex present (diminished) evidence of? ↑ Sexual dimorphism! ♀ : ~3.5 ft., ~65 lbs. ♂ :4.5-5 ft., 110-130 lbs. Foramen magnum: low & well centered

14 A. afarensis: Lucy I.M.I: higher than modern humans, meaning? Arms slightly longer & legs shorter relative to us Pelvis: illium: short, broad & curved Presence of femoral angle Big toe: semi-divergent, not much of an arch Famous specimen: Lucy! Why famous? (then) most complete specimen found! Origins of her name? Lucy in the Sky w/ Diamonds (Beatles L.S.D….what a trip!

15 Visual comparison of skeletal features Footprints @ Laetoli site: made by A. afarensis footprints.html

16 A. afarensis: Dikika Baby Only ~3 yrs old at death, cranium: over 90% complete! (hyoid bone, still ape-like) (length of the vocal cords & connection w/ human speech) “Lucy’s baby”, though lived ~150k yrs. before Lucy! & Video

17 Other Australopithecines A. africanus: S. Africa, gracile, 3-2 m.y.a. Lumpers vs. splitters debate: Genus Paranthropus A. (or P.) aethiopicus: E. Africa, 2.8-2.2 m.y.a., famous find named “Black Skull” (color: mineralization) Dubious distinction: smallest adult human brain ever found…(& you thought we’d already found it)

18 Australopithecines cont’d A. (or P.) boisei: E. Africa, 2-1 m.y.a., “super robust”: extremely pronounced robust features (Back to geologic time pwrpt)

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