[Taxacom] chimp-human interbreeding & fuzzy origins?

Ken Kinman kinman at hotmail.com
Tue May 23 22:49:27 CDT 2006

Dear All,
       As I stated in December 2004, I have been increasing inclined to 
place Sahelanthropus before Pan, rather than after it.  Therefore, I am here 
switching the two (Sahelanthropus splitting off immediately before Pan, 
rather than immediately after it).  However, Sahelanthropus could eventually 
slide down even further, either clading with Gorilla (as a sort of 
proto-Gorilla as favored by Brunet), or splitting off just before Gorilla 
(perhaps making Sahelanthropus the closest thing we have to an ancestral 
member of the African greater ape clade.  In any case, they will all 
continue to be members of Family Pongidae in my classification.

       9  Proconsulidae
       ?  Oreopithecidae
      10  Hylobatidae
      11  Pongidae% (sensu lato)
            1  Dryopithecus
            ?  Ouranopithecus
            2  Lufengpithecus
            B  Sivapithecus
            C  Khoratpithecus
            D  Pongo
            3  Gorilla
            ?  Samburupithecus
            4  Sahelanthropus
            5  Pan
            6  Orrorin
            B  Ardipithecus
            7  {{Hominidae}}
     _a_  Hominidae
            1  Australopithecus% (sensu lato)
           _a_ Homo

            Ken Kinman
>From: "John Grehan" <jgrehan at sciencebuff.org>
>To: "Barry Roth" <barry_roth at yahoo.com>, "TAXACOM" 
><taxacom at mailman.nhm.ku.edu>
>Subject: Re: [Taxacom] chimp-human interbreeding & fuzzy origins?
>Date: Tue, 23 May 2006 09:14:31 -0400
>Barry Roth wrote:
> >   (2)  if the Toumai skull, which is said to combine features of both
> > humans and chimpanzees, precedes the definitive human-chimp split
>Patterson et al claim (p. 4) that "The Toumai fossil (Sahelanthropus
>tchadensis), with its bipedalism and hominin dental features, is usually
>interpreted as being on the hominin line...".
>Both features are problematic to say the least. The bipedalism is
>inferred only through modeling and extrapolation that ignores similar
>positional characteristics of the foramen magnum in non-bipedal
>primates. As for "hominin" dentition one might wonder what that would
>be. Two papers are cited.
>The first is Brunet et al (2002). This paper is rather tricky when it
>comes to explicit hominin dental characters. On page 146 they
>distinguish Sahleanthropus as a hominid from large [note the caveat]
>living and known fossil hominoid genera in various respects, but do not
>specify in what way such differences constitute hominid synapomorphies.
>For example (p. 146), they note that the cheek-teeth enamel is thinner
>that Homo, but thicker than chimp. For orangutans they just say to see
>further into the article.
>On. P. 150 they say that a lower c-P3 diastema is absent and therefore
>Sahelanthropus "probably represents an early stage in the evolution of
>the non-honing C-P3 complex characteristic of later hominids". The only
>trouble is that Australopithecus afarensis does have a diastema, So if
>Sahelanthropus is diagnostically hominid through absence of a diastema,
>then afarensis is diagnostically not a hominid at all.
>Finally on p. 151 they refer to derived hominid dental features as (1)
>non-honing cupper canine-third upper premolar complex (problematic as
>above), and intermediate postcanine enamel thickness. It is this enamel
>thickness that is problematic. Humans and orangutans have thicker molar
>enamel overall than chimps or gorillas. Sahelanthropus is supposed to
>have enamel "intermediate" enamel thickness. Intermediate between what?
>I have to infer that it is between chimps and Australopithecus because
>that seems to be the only comparison given (bottom right column p. 150.
>The implication seems to be that anything "intermediately" thicker than
>chimps but thinner than australopiths is diagnostically hominid. That
>would make the orangutan hominid because they also have thick molar
>enamel. One of the authors (Pilbeam) in other publications claims that
>the ancestral largebodied hominoid had thick enamel so it got thinner in
>chimps. If that is the case an "intermediate" thickness must also
>represent a derived state since the thick enamel of hominids
>(Australopithecus, Homo) is primitive.
>So if the above dental features are anything to go by there is nothing
>to suggest Sahelanthropus is hominid. The authors also claim that
>Sahelanthropus is similar to later hominids in having a large continuous
>supraorbital torus. Now this one I will dare to call "garbage" as an
>accurate description because no australopiths have the continuous
>African ape torus (and also lack the continuous sulcus), and in Homo it
>(or at least a similar structure) is present only for some fossils
>currently assigned to Homo erectus (and the torus of Sahelanthropus
>looks like no other hominoid at all - very autapomorphic). And in
>afarensis the supra-orbital tori and more robust than in orangutans, but
>otherwise they follow the same configuration as mounded structures over
>each eye orbit.
>The other paper is Vignaud et al (2002) and in a quick read I did not
>see anything substantiating hominid dental characters.
>I do wonder about the quality of this kind of hominid study. Would I be
>justified to say that a lot of it is "garbage"? Perhaps according to the
>third author of the Sahelanthropus paper - David Pilbeam - who in other
>publications has said that morphology is completely untrustworthy - and
>yet the authors ask us to trust their morphological work as scientific
>in accepting their hominid claims.
>If anyone can refute my above contentions I would be very interested (I
>may not be happy to be wrong, but very interested nonetheless).
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