Re: Siva, Giganto & Pongo
Harry Erwin (herwin@gmu.edu)
Mon, 31 Jul 1995 20:02:48 -0400
In article <3v73ji$i9k@geraldo.cc.utexas.edu>, Alex Duncan
<aduncan@mail.utexas.edu> wrote:
> In article <3v31p4$pml@portal.gmu.edu> HARRY R. ERWIN,
> herwin@osf1.gmu.edu writes:
>
> >: >G. seems closer to Pongo.
> >: >
> >: Than Siva? What synapomorphies aren't also present in Siva?
> >
> >This one surprised me the first time I saw it, too. I know you're an
> >expert on this clade, so I'd be interested in your opinions here. The
> >database splits the clade at this point based on male weight--a heavy
> >group (P and G starting at 70 kg and going up to 140 kg) and a lighter
> >group (heavy and light Sivapithecus and Lufengpithecus in the 40-50 kg
> >range, which was fairly nominal for ground apes of that time). I've tried
> >to minimize the importance of weight, but these differences are
> >significant. Note that there are other features that the database says
> >_could_ have been synaptomorphies, but I trust them even less.
>
> There are several aspects of this that trouble me. The first is using
> body size as a character. I believe Cope's law states that most
> mammalian lineages will tend to increase in body size during their
> history. While this can only be regarded as very general observation, it
> does point out that body size increase happens frequently, in different
> lineages, and should only very cautiously be considered a synapomorphy.
> I suspect that body size can either increase or decrease quite rapidly
> within a lineage. For example, it seems that a lot the Pleistocene
> "sub-fossil" orangs were larger than the extant species.
I turned off body size and it still linked Pongo with G. Body size
differences of the magnitude we're dealing with here don't happen easily.
>
> This is also a little troubling because some Siva species have males at
> least as large as male Pongo (see S. parvada, for instance).
The database thinks Sivapithecus started out small (about 'Ramapithecus' size).
>
> The main reason that this disturbs is that nothing but dental and
> mandibular characters are known for Gigantopithecus. It seems a safe
> assumption that characters that are present in Siva & Pongo would also be
> present in Giganto, but this is assuming what we're trying to prove, and
> a little circular.
Yes, but there are some dental and mandibular features of Siva. that the
database thinks were derived and Pongo primitive. Premolar row length,
mental foramen height, max alveolar index, P^3 crown shape, molar size
heteromorphy. Also, associating Pongo and Gig. on their own branch keeps
the root of the Pongoid clade relatively close to the ancestral line
(parsimony).
>
> Siva has a number of potential synapomorphies shared w/ Pongo, including
> orbital shape, interorbital distance, airorynch cranium, etc. More
> importantly, there is one character that is almost certainly a good
> synapomorphy -- the way the premaxilla overlaps on the palate and the
> related extremely small caliber incisive foramen. This character remains
> unknown for Giganto, and thus the safest thing to do w/ Giganto may be to
> place it in an unresolved trichotomy w/ Siva & Pongo. Or, depending on
> how you view the polarity of enamel thickness, it might be a good sister
> group for Siva.
It predicts that Gig. will turn out to share those synaptomorphies.
>
> One could even argue on the basis of body size that Giganto is TOO
> derived to be a sister group for Pongo.
Unless Pongo is the less specialized of the two in _weight_. Remember,
Pongo already fist walks, and if it really definitely adopted terrestrial
ways, you'ld soon have a big knuckle-walker.
--
Harry Erwin
Internet: herwin@gmu.edu
Home Page: http://osf1.gmu.edu/~herwin (try again if necessary)
PhD student in comp neurosci: "Glitches happen" & "Meaning is emotional"
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