Re: Orangs as Closest

Paul Crowley (
Wed, 07 Aug 96 23:32:38 GMT

In article <4ua58f$> "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.

> Matthew O. Fraser ( 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.

> 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?

> 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.)