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Re: Differences between *Vancleavea* and thalattosaurs
This is a case of "is" vs "is not." Let's call it "up in the air" for now. Let
someone else come along, employ a sufficient gamut of taxa and nail it down.
You can look at one trait, or a dozen and find archosauriform homologies. What
this requires is a thorough phylogenetic analysis.
Yes I did contact the authors directly.
We could wait for a year or more to see my work published, but why? The news is
now. And thalattosaurs are just a small part of the story I want to tell.
To your individual points:
1. Neither *Miodentosaurus* (using Wu et al. 2009) nor *Askeptosaurus* (using
Müller's PhD thesis, 2002) have thecodont dentition, and neither of them have
interdental plates (which is derived within thecodont jaws, rather than being
present at the same time as thecodonty itself).
The mistake IMHO is with Wu et al. who scored Miodentosaurus as subthecodont
when the lingual dentary is just as high as the labial dentary. Interdental
plates cannot be verified in either taxa given the images presented. Which
author was hedging? We'll have to leave this one for later. It is also very
possible, Vancleavea arrived at (or never lost) tooth dividers independently.
After all, it's not far from Helveticosaurus. Not sure what it's status is,
but given such big teeth, evolution might have added some support there.
2. <lack of post-axial intercentra - also in Miodentosaurus Askeptosaurus>
None are apparently ossified in either *Miodentosaurus* nor *Askeptosaurus*,
3. In this case, *Askeptosaurus* does have an offset femoral head, but
*Miodentosaurus* does not.
Okay. Evolution marches on.
4. *Miodentosaurus* (Wu et al., 2009) lacks the sigmoidality you infer, while
*Askeptosaurus* does possess this aspect.
Okay. Evolution marches on.
5. lack of intertrochanteric fossa on femur. Unfortunately, as above, this
seems to be a *Miodentosaurus* = no, *Askeptosaurus* = yes issue.
Okay. Evolution marches on.
In thalattosaurs the trend seems to be from short snout to long snout, long
teeth to short teeth, armor to naked, feet to fins, etc. We'll have to see how
it all falls out when all the details come out.
In the meantime, if Vancleavea is indeed an archosauriform, don't you wonder
where the antorbital fenestra and the temporal fenestrae disappeared to
(without a trace)? Where's the mandibular fenestra? Why is the orbit in the
front half of the skull? Then remember, "the apple doesn't usually fall far
from the tree" which is another way of saying evolution works in small
incremental steps. There is a smaller number of steps needed to nest Vancleacea
in one branch than another.
I get the impression that you are "defending the status quo" by noting that you
chose to report on only those few minor characters that would tend TO support
the Nesbitt et al. results, rather than say, "attaboy, Dave!" and report on all
the major traits (see above) that tend to NOT support the Nesbitt et al.
results. I judge referees the same way. If they have nothing "nice" to say
about several months worth of work, then they probably have a personal agenda.
The good ones weigh the good against the bad.
Hang in there, and best wishes,
On Dec 6, 2009, at 3:07 AM, Jaime Headden wrote:
> First, Dave: Where do you get the impression I am "protecting the status
> quo"? Such a statement does follow when someone tries to argue that their
> work is just as important to the "status" as any fringe concept, like ESP or
> Deepak Chopra. This doesn't invalidate the fringe concept, but it certainly
> does stress the attitude in approaching people who, like me, prefer to put
> their "money" where the published data lies. So far, your work is
> unpublished, and you've not yet taken the approach some of us have requested
> of you, in talking to the original authors in verification and publishing
> your own work. It makes the whole process a LOT easier.
> Second, I am not specifically noting features myself (David Marjanovic did)
> but citing the papers that redescribe *Vancleavea campi*. Personally, looking
> at the ilium, it can sure look a lot like a non-archosauromorph/iform ilium,
> if it were only certain what is an archosauriform when taxa like
> proterochampsids, drepanosaurs, et al. all seem to shift in and out. Tweaking
> with the content resolves separate features diagnosing each node, and this is
> especially true when one radicalizes the topology and uses it to test the
> veracity of other phylogenies (rather than using other phylogenies to test
> Jaime A. Headden
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> "Human beings, who are almost unique in having the ability to learn
> from the experience of others, are also remarkable for their apparent
> disinclination to do so." --- Douglas Adams (Last Chance to See)
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion
>> Subject: Re: Differences between *Vancleavea* and thalattosaurs
>> From: firstname.lastname@example.org
>> Date: Sat, 5 Dec 2009 15:11:48 -0600
>> CC: email@example.com; firstname.lastname@example.org
>> To: email@example.com
>> All well and good Jaime.
>> Let's take your points one at a time:
>> thecodont dentition - also in Miodentosaurus Askeptosaurus
>> interdental plates -- also in Miodentosaurus Askeptosaurus
>> lack of post-axial intercentra - also in Miodentosaurus Askeptosaurus
>> femur with medially inflected head - from Nesbitt et al. 2009: "The proximal
>> head is poorly defined, being expanded but continuous with the shaft."
>> sigmoidal femoral shaft - also in Miodentosaurus Askeptosaurus, but to your
>> point, maybe not so much.
>> lack of intertrochanteric fossa on femur - also in Miodentosaurus
>> presence of osteoderms - a-ha! got me... except the outgroup includes
>> placodonts, so there you go.
>> Check out the literature. Miodontosaurus in particular.
>> While it is sometimes important to protect the status quo, some things just
>> ain't so.
>> David Peters
>> On Dec 5, 2009, at 2:35 PM, Jaime Headden wrote:
>>> In addition to all this, following Parker and Barton (the OTHER paper on
>>> *Vancleavea campi*), *V. campi* also possesses thecodont dentition,
>>> separate and distinct interdental plates (also contingent on but elaborate
>>> to the presence of thecodonty), and (P&B, p.13):
>>> "Unambiguous synapomorphies supporting the inclusion of *Vancleavea campi*
>>> into Archosauriformes include the lack of post-axial intercentra, a femur
>>> with a medially inflected head, a sigmoidal femoral shaft, the lack of a
>>> distinct intertrochanteric fossa on the proximoventral surface of the
>>> femur, and the presence of osteoderms."
>>> Despite *V. campi* being _another_ apparently aquatically derived taxon
>>> (such that it SHOULD resemble things like pachypleurosaurs, mesosaurs,
>>> nothosaurs, metriorhynchoid crocs, etc.) *V. campi* is distinguihsed from
>>> them by a host of features that ensures that it is not, in fact, a
>>> nonarchosauriform diapsid. That is at least based so far on the two
>>> cladistic analyses to included it with the new data (Parker and Barton,
>>> 20009 and Nesbitt et al., 2009).
>>> Parker, W. G. and B. J. Barton. 2009. New information on the Upper Triassic
>>> archosauriform *Vancleavea campi* based on new material from the Chinle
>>> Formation of Arizona. _Paleontologica Electronica_ 11(3)[14A]:20p.
>>> Jaime A. Headden
>>> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>>> "Human beings, who are almost unique in having the ability to learn
>>> from the experience of others, are also remarkable for their apparent
>>> disinclination to do so." --- Douglas Adams (Last Chance to See)
>>> "Ever since man first left his cave and met a stranger with a
>>> different language and a new way of looking at things, the human race
>>> has had a dream: to kill him, so we don't have to learn his language or
>>> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion
>>>> Date: Sat, 5 Dec 2009 14:48:12 +0100
>>>> From: firstname.lastname@example.org
>>>> To: email@example.com
>>>> Subject: Differences between *Vancleavea* and thalattosaurs
>>>> Judging *Vancleavea* from the illustrations here:
>>>> - Thalattosaurs retain the supratemporal. *Vancleavea* lacks it.
>>>> - Thalattosaurs have an open lower temporal arch (the caudal process of
>>>> the jugal doesn't reach very far back, so the lower temporal fenestra is
>>>> open ventrally); I'm not even sure if they have a quadratojugal at all
>>>> (none is in any case preserved in *Miodentosaurus*). It's closed in
>>>> *Vancleavea*, the qj is large, and the caudal process of the j is very
>>>> broad dorsoventrally, much unlike the very delicate T-shaped jugals of
>>>> - The maxilla contacts the naris in thalattosaurs. In *V.*, they are
>>>> separated by a huge caudodorsal process of the premaxilla.
>>>> - Thalattosaurs have a very large pineal foramen. *V.* lacks any trace
>>>> of it.
>>>> - Thalattosaurs retain caudal ribs -- real free mobile ribs on the first
>>>> few tail vertebrae. Can't see such a thing in the low-resolution
>>>> reconstruction of *V.*.
>>>> *V.* shares all these character states with all other archosauriforms,
>>>> except for the thin jugal of... maniraptoriforms or something.
>>>> Both, however, have a single bone called the "postorbital" in *V.* and
>>>> the "postfrontal" in thalattosaurs... The quadrate looks similar, too,
>>>> differing from the pillar dinosaurs have, but I'm not familiar with
>>>> enough diapsid quadrates to tell what that means.
>>>> - In thalattosaurs the rostral margin of the orbit is formed by the
>>>> maxilla. In *Vancleavea*, the prefrontal does that, and (perhaps because
>>>> the orbit is so remarkably small) it even contacts the jugal, excluding
>>>> the maxilla from the orbit altogether. Or is the "prefrontal" of *V.*
>>>> actually the lacrimal, which is altogether missing in thalattosaurs (or
>>>> at least *Miodentosaurus*)?
>>>> - *V.* has very long hemal spines. Thalattosaurs never.
>>>> - *V.* has considerably smaller limbs, especially hands & feet, than
>>>> Finally, *V.* is much smaller than *Miodentosaurus*. This means that
>>>> things like the relatively much smaller orbit of *V.* (complete with
>>>> taller jugal and maxilla) or its relatively much shorter extension of
>>>> the jaw joints caudal to the occiput cannot be size-related -- the
>>>> opposite relationship would be expected.
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