Re: Dissecting the Aquatic Ape: Bipedalism

HARRY R. ERWIN (herwin@osf1.gmu.edu)
29 Jul 1996 01:12:59 GMT

Paul Crowley (Paul@crowleyp.demon.co.uk) wrote:
: In article <4t0ljo$hts@portal.gmu.edu>
: herwin@mason2.gmu.edu "HARRY R. ERWIN" writes:

: > : / - - - - - Knuckle-walker(s)
: > : {a} Ancestral Ape <
: > : \_ _ _ _ _ _ Bipedal hominid
: >
: > : {b} Ancestral Ape - - -> Proto-chimpanzee - - - -> Chimpanzee
: > : \_ _ _ _ _ _ _ > Bipedal Hominid
: >

: > Last I checked (February), the split was still a bush. I did read a good
: > article (November) that argued (based on sequencing data) that the three
: > lineages diverged within a couple of hundreds of thousands of years,
: > hence effectively simultaneously.

: Did this split happen at the same time (or shortly after) the
: Ancestral Ape descended from the trees to become largely territorial?
: The likelihood must be reckoned to be small.

Dryopithecus, which was an early orthograde below-branch feeder with
little evidence for terrestrial movement, dates to about 10 MYr BP, close
to Ankarapithecus and Ouranopithecus. The split between the hominids and
Pan and Gorilla is estimated to date to about 7 MYr BP. We have bipeds by
4 MYr BP.

: The niche for a ground-living large ape, that used trees for food
: and for nocturnal refuge, had been available for tens of millions
: of years. Surely the probability must be that it was exploited
: for several million years before the split occurred. The finding
: of Ankarapithecus Meteai must support this. A species that had
: adapted to this niche would have become widespread throughout
: tropical Africa and probably beyond. (Turkey is nowhere near the
: tropics.)

The evolution of orthograde locomotion in the lineage leading to Homo was
about 10-12 MYr BP. Prior to that, ground-dwelling apes would have been
pronograde (read like a catarrhine monkey). The earliest catarrhines we
have evidence for were about 18 MYr BP, simultaneous with a number of
early relatives of Proconsul, some of which were probably as terrestrial
as a chimp. The niche was in use, but not by orthograde hominoids.

: The split would have resulted from small populations of this main
: species becoming isolated. So which was the (widespread) parent
: species? It certainly wasn't the hominid branch. Was it the
: chimpanzee or the gorilla? Can DNA studies provide indications
: of genetic variability to the extent that, say, an 10 Myr-old
: species could be distinguished from a 6 Myr-old one? Have any
: such studies been attempted? For example, how far back are the
: chimpanzee and gorilla "Eves" and "Adams"?

See above. My point is that there were ground-dwelling large apes when
our ancestors were spending almost all of our time in the trees.

: Paul.

--

Harry Erwin, Internet: herwin@gmu.edu, Web Page: http://osf1.gmu.edu/~herwin 

49 year old PhD student in computational neuroscience ("how bats do it" 8)

and lecturer for CS 211 (data structures and advanced C++)