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Re: Differences between *Vancleavea* and thalattosaurs
Okay, my cards are on the table. Characters below shared with
Askeptosaurus OR Miodentosaurus or both (quite a variety between
them!) and not shared with proterochampsids AND erythrosuchids (the
bounding taxa for Vancleavea, sensu Nesbitt et al.)
2. Nasals separated by premaxilla ascending process (that's the
"neomorph" in Vancleavea and the related: Premaxilla contacts
You identified two correlated characters. :-) But what makes you so sure
the neomorph is separated from the pmx only by a break? Don't you think
that's the first thing Nesbitt et al. would have thought of? If you have
the fossil in front of you, it's possible to distinguish sutures from
Apart from the fact that the pmx touch it, the neomorph reminds me of
the interfrontonasal found in *Eryops* and the "microsaur" *Crinodon*
(if that's not a dorsal exposure of the sphenethmoid, a regular
occurrence in frogs).
3. Frontals longer than nasals
Just make sure this isn't counted already (as a ratio of snout length to
postorbital skull length or something).
5. Upper temporal fenestra closed or slit-like and the related:
Postorbital-parietal contact long (extensive)
Again, you demonstrate you're fully capable of identifying correlated
6. Parietal skull table broad
Is it broad, or is it short? Broad relative to what?
8. Mandibular fenestra absent
Might be correlated to a strong bite, see tyrannosaurs. That would mean
that presence/absence of the mandibular fenestra is only applicable to
taxa with weaker bites.
9. Cervicals decrease in size anteriorly
Are you sure that's not a consequence of the relatively small skull?
10. Metacarpal II is the longest metacarpal
In us, too. No idea why.
11. M4.3+m4.4 fused
Impossible to find out without the fossil in front of you, and probably
impossible even then.
Also, why did you (offlist) reconstruct the hand with a phalangeal
formula of 2-3-4-4-4 instead of 2-3-4-5-3? The latter has the same
number of bones and is way, way, way less freaky.
13. Metatarsals II-IV not shorter than half the tibia
Probably correlated to an aquatic lifestyle.
14. Metatarsals I and V are wider than II, III and IV
Assuming you identified them all correctly.
15. Pedal digit IV not narrower than III
Granted, other than these characters, between Erythrosuchids and
Proterochampsids, one or the other includes one character or another
of Vancleavea, which in itself is amazing, but are we sure we don't
know any intervening taxa between the erythros and proterochampsids?
The Early Triassic archosaur record isn't as good as I'd like it to be.
Except maybe in Russia which is crawling with supposed proterosuchids,
erythrosuchids, and even rauisuchians that almost nobody has ever looked at.
Finally, I reduced my taxon list to match Nesbitt, et al. 2009. +
Doing nothing else the tree resulted in 499 steps. [...]
moving the Proterochampsids to the Nesbitt order results in 510 MPTs
moving Sphenosuchus to the Nesbitt order results in 518 MPTs moving
Vancleavea to the Nesbitt order results in 566 MPTs removing
Askeptosaurus from inclusion so the set matched the Nesbitt set
results in 505 MPTs
moving Vancleavea to the outgroup or just inside Mesosuchus, where it
nested originally resulted in 492 trees and moving Vancleavea between
Proterosuchus and Erythrosuchus resulted in 501 trees.
Why do you bother giving us the number of trees? I don't see what your
Surely you don't mean it as some kind of support measure...?
Also, I notice you didn't address my question as to whether you knew the
difference between ordered and irreversible characters. That's important
because, as long as you don't know this, you basically can't do
phylogenetics yourself or understand how other people do it.