hominid classification

[John Grehan]

At 10:16 PM 8/8/04 -0500, Ken Kinman wrote:
>Dear All,
>       Having read John Grehan's comments and having read more on the
> recent debate on hominid origins, I am seriously considering transferring
> Sahelanthropus, Orrorin, and even Ardipithecus, to Pongidae (although
> still as the closest outgroups to Hominidae).

On the basis of what characters?

>This would leave Family Hominidae with only two genera, Homo and
>Australopithecus.  Australopithecus includes as synonyms Kenyanthropus,
>Praeanthropus, and Paranthropus (along with some other older generic
>names).  Recent attempts to revive genus Praeanthropus are highly
>destabilizing and paraphylophobic nonsense that I find extremely
>disturbing (and this taxonomic move should be strongly resisted).

On what basis?


>      Hopefully recently discovered (but yet undescribed material) of
> Ardipithecus will verify it's bipedality, thus bolstering it's placement
> in Hominidae.

If bipedalism is the (only?) basis for Hominidae then what about Orrorin?

>The recent raising of Ardipithecus kadabba (as a separate species from
>Ardipithecus ramidus) earlier this year, along with its significantly
>older age (about 1.2 million years older) could conceivably even throw
>kadabba into a separate genus (either new, or part of Orrorin, or even
>Sahelanthropus?).  It really depends on what the undescribed material (and
>yet to be discovered material) shows.

And it depends on what characters one uses. The teeth of Orrorin and
Ardipithecus are apparently not the same with respect to dental thickness
and height of molars.


>      No matter what happens, a paraphyletic Australopithecus giving rise
> to genus Homo is unavoidable (even desirable in my opinion).

Why?

>Attempts to completely cladify hominids will always result in unnecessary
>oversplitting, controversy, confusion, and instability.  As John Grehan
>has noted, more rigorous cladistic analysis is needed to clear up this
>mess, but a rigorous (strictly) cladistic classification is an exercise in
>paraphylophobic futility.

In which case a rigorous cladistic analysis would not clear up the mess.


>      Here's the modified classification I am considering until the
> bipedality of Ardipithecus is better established.  I continue to assume
> that the thinning of molar enamel (intermediate in A. kadabba and thinner
> yet in A. ramidus) is in parallel with that of genus Pan (perhaps due to
> a similar shift to feeding on softer foods).

I agree with this. Its purely an assumption to maintain the pre judgement
(based on genetic sequence similarity) that Homo and Pan are sister groups
and also an assumption that selection is the basis of adaptation.


>Of course, if genetic evidence is found to support Grehan's hypothesis of
>closer Pongo-Hominidae relationships, I will have to recode the taxa
>within Pongidae to reflect that, but I haven't seen any such genetic
>evidence presented to date.

The genetic prejudice is irrelevant to the fossil problem.

Why is Orrorin not grouped within Hominidae if it is bipedal and has the
dental characters of humans (and orangutans) with respect to both thick
dental enamel and flattened molar surface?

John Grehan


>   1  Cercopithecidae
>   2  Propliopithecidae
>   3  Pliopithecidae
>   4  Proconsulidae
>   ?  Oreopithecidae
>   5  Hylobatidae
>   6  Pongidae%
>         1  Dryopithecus
>         ?  Ouranopithecus
>         2  Lufengpithecus
>         B  Sivapithecus
>         C  Pongo
>         3  Gorilla
>         ?  Samburupithecus
>         4  Pan
>         5  Sahelanthropus
>         6  Orrorin
>         B  Ardipithecus
>         7  {{Hominidae}}
>  _a_ Hominidae
>         1  Australopithecus
>        _a_ Homo