Skeletal Features of Bipedalism Professor Janaki Natalie Parikh profjnp@gmail. com
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 (? )
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
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
Bipedal pelvis cont’d • Chimp’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
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 • http: //www. npr. org/templates/story. php? story. Id=128245649 http: //www. ted. com/index. php/talks/susan_savage_rumbaugh_on_apes_that_write. h tml Now, back to geologic time pwrpt) •
Robust vs. Gracile Grade Hominids Robust Gracile • Large jaws (buttressed mandible) • Smaller jaws, no buttressed mandible • Molarized premolars & lrg molars (grinding teeth) • Smaller back teeth
Robust vs. Gracile Grade Hominids Robust • Jaws muscles anchored on top (sagittal crest) Gracile • Jaw muscles anchored on the side (no sag. Crest)
Robust vs. Gracile Grade Hominids Robust Gracile • Flaring zygomatic arches • Cranial capacity? • No flaring zygom. Arches • Smaller cranial capacity • Larger cranial capacity
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.
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!
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
Australopithecus afarensis • • 4 -3 m. y. a. , E. Africa, gracile Features: Mixture of human & ape like traits face: prognathic like a chimp Teeth: CP 3 complex present (diminished) evidence of? ↑ Sexual dimorphism! ♀: ~3. 5 ft. , ~65 lbs. ♂: 4. 5 -5 ft. , 110 -130 lbs. Foramen magnum: low & well centered
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! • • http: //www. youtube. com/watch? v=A 7 F 2 X 3 r. SSCU
Visual comparison of skeletal features Footprints @ Laetoli site: made by A. afarensis http: //science. discovery. com/videos/100 -greatest-discoveries-shorts-laetolifootprints. html
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 ~150 k yrs. before Lucy! • http: //www. sciencedaily. com/releases/2006/09/060920193509. htm • http: //ngm. nationalgeographic. com/2006/11/dikika-baby/sloan-text & Video
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)
Australopithecines cont’d • A. (or P. ) boisei: E. Africa, 2 -1 m. y. a. , “super robust”: extremely pronounced robust features • http: //www. npr. org/templates/story. php? story. Id=128245649 • (Back to geologic time pwrpt)
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