Re: Bidpedalism

4 Jun 1995 22:23:53 GMT

Gerrit Hanenburg ( wrote:
: In article <3qki2g$> (HARRY R. ERWIN) writes:

: >I ran into an interesting book by Oxnard on the postcranial adaptions of
: >primates and australopithecines. The evidence is fairly strong that their
: >motor behavior was like nothing known today. You can deduce that they
: >probably were bipedal on the ground, but spent most of their time moving
: >arboreally in the trees. H. habilis seems to be similar.

: I didn't read Oxnards book and maybe my comment is premature, but how
: much can we deduce from anatomy alone?

Not as much as we'd like. Oxnard is very careful and through.

: The hindlimb of AL 288(Lucy) was short both absolutely and relative to
: forelimb and trunk lengths;this would have affected stride length and
: walking velocity.

Yes. The ratio for AL 288 was about 0.85. ON-62 was about 0.95. A.
afarensis was 0.8-0.9 including all the data. A. robustus and boisei were
about 0.75, and KNM-ER 15000 was 0.738. African apes run from 0.95 to
1.20. We're in the range 0.7-0.75.

: The hindlimb joint sizes are bigger than those of apes but much smaller
: than modern humans even when differences in overall body size are taken
: into account;this suggests less complete adaptation to full weight
: bearing by the hindlimb.

Beyond that, their elbows had less mobility than ours, while the knees
had significantly more.

: Locomotor reconstructions based on the Laetoli footprints suggest a
: relatively short,but not necessarily slow,stride pattern to early
: hominid bipedalism.

That's to be expected for a shorter pendulum length.

: The anatomical evidence suggests australopithecine ground locomotion
: was bipedal,but not necessarily of modern human form.
: So much seems to be clear.


: The anatomy of the upperlimb,such as the more cranially oriented
: glenoid cavity and the curvature of the phalanges may indicate arboreality.

Oxnard has evidence that the curvature approximated that of Pongo and was
markedly greater than that seen in Gorilla and Pan.

: But from this you cannot deduce that they probably spent most
: of their time moving arboreally.Chimpanzees are anatomically adapted
: to arboreality but they spend most of the daytime on the ground.

Interestingly, their hands are adapted to knuckle-walking (with the
involved bones forming a straight-sided triangle to handle compressive
stress) and not to climbing (where the extension stress is minimized by
bone curvature).

: I'm curious about Oxnards anatomical evidence.

Take a look. He seems fairly solid.

: Gerrit.

Harry Erwin
PhD student in comp neurosci: "Glitches happen" & "Meaning is emotional"