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RE: Differences between *Vancleavea* and
Tim Williams wrote-
> Hi Mickey
> Can you re-send in plain text?
Oops. Forgot to switch to that. Ironically, my message was something Jaime
wrote that he couldn't send to the DML due to connection issues. I have no
side in the present case, as my knowledge of diapsid systematics and
thallatosaur anatomy is poor. I will note that I don't have an issue
philosophically with someone challenging even a detailed paper by experts when
it comes to phylogeny, as people do poor phylogenetic work more often than
realized. I also think that diapsid phylogeny is comparatively untested, where
people mostly use the same characters (and always leave out many taxa) which
are designed to support the 'known' clades. On the other hand, Peters has
shown that he doesn't know how to do a proper phylogenetic analysis (ordering,
correlated characters, etc.), so even ignoring his sketchy Photoshop method I
don't trust his analysis at all. The way he initially presented it, as a mere
statement that the authors were wrong, is ineffective regardless. Lately it's
been improving, as people are discussing individual characters and how they
vary. And on to Jaime's original message-
Pardon me for my previous comments on *Askeptosaurus*. I was mistaken on a few
features, and misidentified a couple of aspects in differentiating it from
*Vancleavea* (and from the archosauriform/morph diagnostic characters).
1. *Askeptosaurus* lacks femoral sigmoidality, and the femur is straight in
lateral and cranial views.
2. The femur lacks an intertrochanteric fossa, and the internal trochanter is
positions so high on the head that it is only slightly differentiable; I had
mistaken this for the femoral caput, and this also indicates that:
3. The femoral head is not inflected medially, and there is no caput; the
proximal femur articulates directed into the acetabulum, and is apparently
oriented at a right angle to the body wall (as in other highly aquatic diapsids
including some nothosaurs, pachypleurosaurs, ichthyosaurs and mosasaurs.
Futhermore, *Askeptosaurus* possesses a fenestra between the parietal,
squamosal and postorbital, resulting in a "intromittent" surpatemporal
fenestra, which reflects on the potential for closure of the fenestra within
Thalattosauria and not prior to the thalattosaurian ancestor.
One could also discuss a laundry-list of features by which thalattosaurians and
*Vancleavea* differ, but I will expound primarily on the most apparent:
1. The quadrate of *Vancleavea* possesses a long, triangular pterygoid process,
which is short or absent in *Miodentosaurus* and *Askeptosaurus*.
2. As David Marjanovic noted, *Vancleavea* appears to lack a pineal foramen,
and this is notable because despite the separation of the parietals from one
another in the Ghost Ranch specimen, no channel for the foramen is apparent on
the medial margins of the exposed parietals. This differs from both
*Askeptosaurus* and especially *Miodentosaurus* as in the latter the foramen is
particularly large and placed between the frontals and parietals.
3. *Vancleavea*, unlike either *Askeptosaurus* or *Miodentosaurus*, preserves a
large, ossified laterosphenoid. I omitted this feature previously (faulty
memory!) but it would be interesting to note its relationship to
archosauromorph phylogeny if the element preserved anterior to the cranial
nerve V opening in basal turtles is indeed a laterosphenoid (and that this does
not provide more evidence for them of being archosauromorphs themselves).
4. Caudal ribs are present on anterior caudals in thalattosaurians, especially
*Askeptosaurus* and *Miodentosaurus*, but absent in *Vancleavea*.
5. The scapula of thalattosaurians is short, rounded and crescentic in aspect,
rather than elongated and rod-like as in *Vancleavea*. The scapula is
particularly interesting as it possesses a distinct acromion, expanded and
crescentic distal expansion, and an offset glenoid which is not offset to the
scapular shaft in posterior view (thalattosaurians thus articulated their
humerus laterally, while *Vancleavea* articulated its humerus posteriorly).
6. *Askeptosaurus* and *Miodentosaurus* have an elongated, spur-like aspect to
the proximal (dorsal) portion of the ilium, where the sacral ribs articulate.
This portion of the bone is horizontally aligned, and does not terminate in a
7. The calcaneum in *Askeptosaurus* is short, blocky, and angular (it is not
preserved in *Miodentosaurus*), as in *Vancleavea*, but in the latter, there is
an elongated process that is perhaps analogous if not directly homologous to
the calcaneal tuber of various terrestrial archosauriforms (and absent in
proterochampsids, drepanosaurs, etc.).
It seems that *Vancleavea* (despite an earlier post claiming otherwise) is not,
in fact, *Miodentosaurus* as a direct comparison from the literature alone
resolves this concern. Nesbitt et al. may be faulted for at most one large
thing in their study, and that is the brevity of the phylogenetic analysis they
performed. This analysis, along with Parker and Barton's, is particularly
small, although the authors considered as likely the question of *Vancleavea*
relative to nonarchosauromorphs well tested by including index taxa that are
unlikely to be archosauromorphs in the study. Other taxa that shift around
appear absent. It would be interesting to actually see a published analysis
attempting to sample a very broad range of diapsids, but at this point none
exists. When this study is produced, *Vancleavea* (and likely *Doswellia*)
would serve as interesting inclusions.