Re: Dinofest Report #2 (and final)

[Jonathon Woolf <jwoolf@erinet.com>]

Jonathan R. Wagner wrote:

> Somebody (pardon me for losing the name) wrote:
> >In his Saturday talk on North American oviraptorosaurs, Hans-Dieter Sues said
> >his research implied that arctometatarsaly arose multiple times,
>         This, of course, agrees with many workers' current interpretations
> of theropod phylogeny. Various hypotheses seem to disagree on the "where and
> when", varying mostly it seems with the position of Troodontidae and
> "elmisaurids".
>
> >and that Arctometatarsalia is not a valid taxon.
>         Note that I assume here that the comments quoted above are an
> accurate reflection of Dr. Suess' talk.

His heavy accent makes it a bit difficult, and I've paraphrased some things, but
that is what I understood him to be saying.

> Arctometarsalia remains "valid" although the concept of all taxa possessing
> an arctometarsus forming a monophyletic group exclusive of all other taxa
> may not.

Let me see if I understand this correctly:

1. Arctometatarsalia was named after, and defined based primarily on, a specific
synapomorphy, the pinched 3rd metatarsal. This feature was thought to indicate a
close evolutionary relationship among these taxa.  The name was therefore chosen
to reflect this relationship.

2. This feature is apparently not synapomorphic among the taxa included in
Arctometatarsalia. Therefore, these taxa are not more closely related to each
other than any of them is to other theropods.

3. Even though the relationship after which the clade was named does not exist,
the clade is still valid.

That makes absolutely no sense to me.

Oh, wait, I forgot.  It's cladistics.  It doesn't have to make sense.

-- JSW