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Re: Brusatte et al. 2008



----- Original Message ----- From: "David Peters" <davidpeters@att.net>
Sent: Saturday, September 13, 2008 7:32 PM


Having seen the paper and supporting materials, I see that Brusatte
et al. 2008 have a very interesting cladogram.

Oh yes, but that's not surprising. Most of the included taxa have never been in a cladistic analysis, and this is the first analysis of archosaur phylogeny in something like nine years (not counting the very small matrix of the *Qianosuchus* paper three years ago, and the nice phylogenetic grass it produced).


It is interesting, however, that crocodylomorphs ( + *Erpetosuchus* + *Gracilisuchus*) and aetosaurs come out as sister-groups, that the ornithosuchids are nested inside the "rauisuchian" clade (as the sister-group of the poposauroids), and that the marine *Qianosuchus* is found as the sister-group of *Ticinosuchus* + *Fasolasuchus*.

1. The [theropod + theropod-like forms] form a clade separate from
[the rest of the dinosaurs + pterosaurs  + 'Crurotarsi.']

Well, yes -- the former is a clade, and the latter is paraphyletic with respect to the former. As has already been said twice, this is utterly standard.


2. The above-named clades all have the low-slung, low-skull, naris-on-
top Proterochampsidae as their closest known sister taxon succeeding
Euparkeria and Erythrosuchus as more distant outgroups.

The clade formed by all of them _together_ (in one word: Archosauria sensu Gauthier et al.) has Proterochampsidae as its sister-group, yes, followed by *Euparkeria* and *Erythrosuchus*. This, too, is utterly standard, as has already been mentioned twice.


3. Scleromochlus, with its teenie-tiny hands and spike like digit V
is the sister taxon to pterosaurs. Sister taxa just outside of this
clade don't have a long manual digit IV or a long pedal digit V
either. In fact, those are hard to find anywhere here [Proterosuchus
is not included]. Was there a miracle in the appearance of wings and
toes? Maybe Hone and Benton can help here.

No miracle here. *Scleromochlus* underwent reductions, and the pterosaurs underwent expansions instead. The MRCA of *S.* + Pterosauria did _not_ look like *Scleromochlus*.


I know all this represent the traditional paradigm. I've seen
variations on this cladogram many times before, so you won't win
anyone over by tossing in refs that suffer from the same problems.

You haven't mentioned a single problem yet.

The big question for you to ponder is this: do all these nestings
make sense in terms of gradualism in evolution? If 'sister taxa'
don't blend morphologically from one to another, isn't that a red flag?

Once again, no. The Triassic -- especially Middle and Early Triassic -- fossil record consists mostly of holes. Get rid of your illusions of completeness already.


There _are_ three things that I find odd about the tree: the paraphyly of the "silesaurids" (*Eucoelophysis*, *Sacisaurus*, *Silesaurus*) with respect to Dinosauria and *Lewisuchus*, the position of *Revueltosaurus* (but we have already been promised it won't stay that way), and the existence of *Stagonosuchus* (I simply didn't know about it). All three deserve further investigation. :-)

Also, adding *Ctenosauriscus* would be interesting, and aren't there supposed "rauisuchians" from the Middle Triassic of Russia? (I'll check tomorrow.)