Skeletal Features of Bipedalism

Professor Janaki Natalie Parikh

jnparikh@verizon.net

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://elucy.org/compant.html

• http://www.ted.com/index.php/talks/susan_savage_rumbaugh_on_apes_that_write.html

Now, back to paleoanthro pwrpt)

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

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

• Flaring zygomatic arches

• Cranial capacity?

• Smaller cranial capacity

Gracile

• No flaring zygom. Arches

• 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 1st!

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: 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

A. afarensis: Lucy• I.M.I: higher than modern humans, meaning?

• Arms slightly longer & legs shorter relative to us

• Pelvis: illium: short, broad & curved (bipedal!)

• 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!

Visual comparison of skeletal featuresFootprints @ Laetoli site: made by A. afarensishttp://science.discovery.com/videos/100-greatest-discoveries-shorts-laetoli-

footprints.html

A. afarensis: Dikika Baby• Only ~3 yrs old at death, 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!

• Most complete fossil find of the century & millenium (though it’s still early! )

• 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

• (Back to geologic time pwrpt)