Re: Time Frame: Early Hominids

30 Apr 1995 15:16:58 GMT

Patricia Lynn Sothman ( wrote:
: HARRY R. ERWIN ( wrote:
: : Patricia Lynn Sothman ( wrote:
: : : JoeBeaver ( wrote:
: : --trimmed--

: : There was a note in Science News (April 22, page 253) that folks working
: : at Sterkfontein (Berger in particular) have found that A. africanus was a
: : good deal more arboreal than A. afarensis. The arms and legs seem to
: : support the hypothesis that the primary locomotor adaptation was
: : suspensory climbing, and the pelvis was more primitive than that in A.
: : afarensis, although advanced in that direction from the apes. The dating
: : is about 2.6-2.9 MY BP.

: : Any clues? H. habilis is believed to have evolved from A. africanus, and
: : my character database seems to support that position without these new
: : data.

: I will attempt to answer this one also. My information comes from
: hearing Berger's two talks in Oakland.

Much appreciated. My database has grown to about 130 characters, and this
will clarify some issues. BTW, when I run my data through Joe
Felsenstein's penny program, A. africanus associates with both the main
habiline radiation and with the base of the Paranthropus group (somewhat
more closely to the latter). Erectus emerges at the base of the habiline
radiation as a separate clade. Afarensis + ramidus are primitive and are
associated as a clade.

: Sterkfontein excavations are currently under the direction of Lee
: Berger. They have found a lot of post-cranial material, which displays
: very interesting morphology. The information about the suspensory
: adaptations come from five shoulder girdle elements recently recovered.
: Those greatly increased the sample sizes. These new elements demonstrate
: a unique morphology: namely, that africanus seemed to be adapted in the
: shoulder region to both suspension and bipedality. The elements display
: morphology commesurate with suspension like stability of the
: gleno-humeral joint, large muscle attachments. Bipedality is inferred
: from the more modern human-like broad inferior angle of the scapula.

: The other talk he gave centered upon the tibial morphology of Stw 514.
: It was found in close association with other fossils attributed to
: africanus, so it is designated as africanus. From all the morphological
: features that they are able to discern on this specimen except ONE, this
: is very chimpanzee-like. From comparisons between 514 and AL-288-1
: ("Lucy"), 514 is more primitive and thus is inferred to have a locomotor
: pattern that is different from afarensis. Berger questions the
: phylogenetic relationship between afarensis and africanus based upon this
: tibial specimen and other primitive morphologies within the new africanus
: material.

Like I indicated above, afarensis + ramidus seem to form a clade. (My son
and I did the measurements on the ramidus characters from the data and
figures in the Nature article, so we're looking forward to the additional
data that are to be released later this year.)

: As far as habilis is concerned. The ONLY specimen which has unquestioned
: association between cranial and post-cranial fragments is OH 62 (there
: are questions about the type specimen, OH 7, and the paratypes originally
: ascribed to habilis, e-mail if you want references) found by Johanson's
: team in 1986, published in Nature in 1987 (327: 205-209). This specimen
: has been basically ignored by most paleanths because of its basic
: weirdness. It dates to 1.7 my, craniodentally been assigned to habilis,
: but postcranially demonstrates very ape-like morphology, especially in
: the relative limb proportions. When comparing the forelimb and hindlimb
: in a index, this specimen falls outside the range of modern humans, well
: above any australopithecine. Basically OH 62 had arms almost as long as
: its legs. So Berger's contention about phylogeny that habilis, or Homo,
: originated from something more ape-like in locomotor patterning is not
: necessarily unusual given the morphology of the only known habilis
: post-crania.

How useful to this discussion is KNM-ER 3735? I agree about the
humerus/femur length ratio issue. OH 62 is the only good evidence I've
been able to find between A. afarensis and H. ergaster, and at 0.95, it's
almost at the Pan trog. value of 1.0-1.1. (Again no data on P. paniscus.)

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