Re: Orangs as Closest
HARRY R. ERWIN (herwin@mason2.gmu.edu)
8 Aug 1996 12:40:52 GMT
Paul Crowley (Paul@crowleyp.demon.co.uk) wrote:
: In article <4ua58f$9el@portal.gmu.edu>
: herwin@mason2.gmu.edu "HARRY R. ERWIN" writes:
: > Remains of primitive
: > gibbons are found in East Africa (Micropithecus about 20 MYr BP),
: Prof Elwyn Simmons of Duke writes on page 207 of the Cambridge
: Encyclopedia of Human Evolution that Micropithecus may be a
: relative of the gibbons, or may just be a primitive catarrhine.
: Given the geography, I'd say you have to go for the latter.
The CEHE is a conservative consensus and a few years old. I've been
tracking this in the professional literature. Simons may still be right.
: > Matthew O. Fraser (mof@prophet.pharm.pitt.edu) wrote:
: > : Surely ancestrial primates were mostly arboreal,
: > : and only later certain groups went down to more terrestrial niches. Most
: > : prosimians and New World Monkeys are entirely arboreal. Presumably they
: > : shared a common ancestor at some point with Old World Monkeys, Apes and
: > : Hominids.
: The fact that most such species are arboreal today does not mean
: that their ancestors were. Ancestor species are most likely to
: be general-purpose, non-specialized and widely spread; all this
: implies terrestriality. Whereas, purely arboreal species are
: likely to get isolated in their own patch of forest, as we see
: with the many species of gibbon and the two species of orang.
Given the anatomical evidence for arboreality in almost all modern and
fossil primates (grasping hands and feet, nails, skeleton adapted to
arboreal locomotion--vertical clinging and leaping using a tail for
balance, above-branch quadrupedalism with a long back and tail for
balance, below-branch suspensory climbing with a short back and no tail),
to claim terrestriality puts the burden of proof on the claimant.
: > The speculation on
: > catarrhine monkeys is particularly interesting. Cheek pouches are
: > regarded as the evolutionary innovation that allowed them to forage on
: > the ground and digest their food in the trees.
: Surely it should be the other way around -- foraging the trees and
: eating it on the ground? Intra-species competition is a much more
: potent selection force than predation, and high quality food that
: can be collected quickly is generally in trees, i.e. fruit and nuts.
: If the species goes around in large troops (as many do) then the
: individuals that can grab the most when they find a fruit-laden tree
: (or branch) will be the ones to leave most descendants.
: What do field observations tell us on this?
Catarrhine monkeys, particularly colobines, are adapted to eating
low-quality, unripe fruit and mature leaves.
: > And we do find highly arboreal colobine monkeys with a discontinuous
: > distribution, where the gaps have not had a continuous closed canopy
: > forest since at least the early Miocene, before the evolution of the
: > colobines.
: Do you mean there are discontinuous distributions within the same
: species of colobine? That would have to have some very special
: explanation. OTOH if you don't mean that, then it's easy to explain
: their distribution as being descendants from species of terrestrial
: colobines. Page 222 of op.cit. describes "Mesopithecus pentelicus,
: a semi-terrestrial colobine of the late Miocene . . of Europe".
: (It looks 100% terrestrial to me.)
That's the general take.
: 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++)
|