Re: Time Frame: Early Hominids
HARRY R. ERWIN (herwin@osf1.gmu.edu)
14 Apr 1995 04:22:59 GMT
Robert Scott (rscott@mail.utexas.edu) wrote:
: In article <3mblv9$q4l@portal.gmu.edu> HARRY R. ERWIN,
: herwin@osf1.gmu.edu writes:
: >A. ramidus is basically a primitive chimp. It was still a tree-dweller
: >(probably more than Pan since it lacks the knuckle-walking adaptation to
: >ground-living). Its bipedalism was primarily postural (since afarensis
: was
: >hardly a runner with those big feet). If you track the changing
: characters
: This is glaringly wrong. There are no fossils in the A. ramidus sample
: with morphologies that say one thing or another re knucklewalking. (A
: possible exception might be inferences on knucklewalking based on degree
: of humeral torsion in the A. ramidus prox. humerus if that torsion can be
: measured.) If anyone is interested, I can add more on humeral torsion.
The cranial base appears to be more consistent with an erect posture than
with the terrestrial quadrupedalism (specialized knuckle-walking) of the
African apes. Knuckle-walkers in general are weird--they don't evolve
often, and when k-w appears, it's because increasing weight has forced
protective measures on a hand specialized for something else than
weight-bearing.
: In article <3mblv9$q4l@portal.gmu.edu> HARRY R. ERWIN,
: herwin@osf1.gmu.edu writes:
: >Apparently
: >something came down from the trees about that time and broke up into a
: lot
: >of small distinct populations. One of those populations quickly evolved
: >into a hot plains dweller, H. erectus, with a much broader distribution,
: >and the rest hung around the wooded savanna until they died out, probably
: >by being outcompeted by erectus in those environments both were trying to
: >exploit. H. erectus could live in the plains or in the savanna; the
: >habilines were dependent on the savanna.
: This is all pretty iffy scenario type stuff, you list some possible
: hypotheses about early _Homo_. The characterization of H. habilis coming
: down from the trees is probably misleading. Australopithecines had
: already been bipedal for some time before early Homo first appears. While
: Australopithecines almost certainly climbed trees, it is quite possible
: that H. habilis did as well. You also leave out H. rudolfensis which is
: also probably a good species.
There's lots of variation in H. habilis, suggesting isolated populations.
H. erectus/ergaster had a much wider distribution. A couple of the (prob.)
female specimens of H. habilis exhibit ape-like ratios of arm and leg
element lengths, curved metacarpels, small stature, and low body weights.
My take is that these individuals were bipedal on the ground and
suspensory in the trees (as were the Australopithecines). There's very
little data on H. rudolfensis (3 good specimens), although I suspect it's
closer to the ancestry of H. erectus than H. habilis in the narrow sense.
A lot of my suggestions (for that is all they are) are based on details
of the Turkana boy.
: I truly wonder about the scenario of H. erectus outcompeting H. habilis.
: 99.999% of all species go extinct -failing to adapt to changed
: circumstances-, why invoke the idea of competition as a special
: explanation. I don't think that there is necessarily strong evidence that
: competition is necessarily a robust explanation for extinctions in
: general. I would support climate change - which can be substantiated with
: evidence - as an explanation of extinction over a hazy notion of
: "competition" 9 times out of ten.
Indirect competition. I've got a paper on this if you want a ref.
: >If you track the changing characters
: >from afarensis back through ramidus back one more step, you get a nice
: >ancestor to the Pan/Gorilla/A./H. clade.
: I would agree here. It strikes me as ironic that for all the hollering
: about "no transitional species" by creationists that the human lineage
: bears so many excellent examples of transitional morphologies and species.
: :-)
: Rob
Cheers--
Harry Erwin
Internet: herwin@gmu.edu
PhD student in comp neurosci: "Glitches happen" & "Meaning is emotional"
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