Re: Dryptosaurus species specifics [long]

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Jaime Headden wrote-

> <However, I wasn't arguing synonymy be rejected because of the low number
> of characters distinguishing specimens, but rather because of the
> (admittedly subjective) low importance of the single character.>
>
>   This is a subjective issue that I do not think matters. That a character
> would appear to distinguish the two, and your argument it is immaterial,
> the buirden is upon you to show how, and then support the lack of
> likelihood the two are distinct.

Didn't I do just that in the section directly below, that you bothered to
leave in, but did not reply to?  Read it again for why I believe the single
distinction is not indicative of a "genus-level" difference.
And regardless of what you think, the subjective importance of character
distinctions does matter when dealing with this type of dinosaurian
taxonomy.  Most often, we have only single specimens to work with, so cannot
rely on consistancy in the distribution of differences, or quantifiable
amounts of difference (as in genetics).  It may be subjective, but it's all
we have.

>   Note the holotype of Tyrannosaurus has a narrower
> > ilial
> > peduncle on the ischium than either AMNH 5027 or RTMP 81.61 (Carpenter,
> > 1990).  But virtually no one recommends these be placed in separate
> > species.
> > That this type of variation is known to be intraspecific in a related
> > taxon
> > strongly suggests it is in Bahariasaurus as well.
>
> <As an aside, it's inappropiate to claim Heckert and others erect
> ornithischian tooth taxa "without comparative positioning of the element
> in a series" when they do try to place each tooth in a certain area of the
> jaw. Basal ornithischian teeth are rather homodont anyway, usually grading
> in a predictable pattern from front to back.>
>
>   I can only hope that this opinion of homodonty applies to just Mickey.
> Those who work on ornithischians, for instance, especially basal forms,
> recognize that there is no such thing as a strict homodonty among
> ornithischians without selecting a few select clades.

Those who read sentences, for instance, recognize I wrote "rather homodont",
as opposed to the strict homodonty you are arguing against.

> For instance, in
> ceratopsids, and iguanodontids, the crowns _are_ relatively homodont, as
> well as in hadorsauroids. However, for nearly the entirety of the
> remainder of Ornithischia, this is not true, but that teeth vary in
> morphology mesial to distal in the jaw, and between jaws, and a crown can
> be identified as to left or right. Not always, but most of the time. But
> this is not really true the more basal you get, where teeth not only get
> more similar among taxa, but further heterodont and vary between upper and
> lower jaws. But there's a point, as in general theropods, that identifying
> a maxillary and dentary crown cannot be done, as in *Lesothosaurus*, in
> which these crowns are identical except for location of the wear facets;
> but these teeth usually lack assymetry or wear facets, and the
> identifications of such crowns and their diagnoses can only be relegated
> to crown shape based on assumptions without jaw placement information.
> Thus, the teeth can belong to similar taxa in which heterodonty was
> rampant. That the authors of said Late Triassic teeth ignore the caveat of
> heterodonty is surprising, given their apparently familiarity with the
> conditions in basal ornithischians and so-called "hypsilophodontians."

I see no arguments against the kind of loose homodonty I was advocating,
where teeth "grade in a predictable pattern from front to back" in most
basal ornithischians.  You see this in fabrosaurs, thyreophorans,
hypsilophodonts, heterodontosaurids, non-ceratopsid marginocephalians, etc..
Basically any ornithischian that existed in the Triassic to Middle Jurassic,
which is when all these tooth taxa created by Heckert et al. lived.  Sure,
some of these taxa have highly differentiated premaxillary dentitions, or
canine-like teeth, but such morphologies are never used as the basis of new
ornithischian taxa.  And yes, some heterodonty exists between upper and
lower crowns, and those that are mesial and distal, but these differences
are predictable as I said.  Ridges will vary in strength, denticles in
number, teeth will be more or less compressed and/or unrecurved.  We have
many taxa with complete articulated dentitions, so we know what to look out
for.  Contrary to what you say, I don't believe any of the Triassic teeth
you debate the validity of are similar enough to each other or to other
established early ornithischian taxa that positional information is needed
for diagnosis.

>    I, personally, see that an unplaced element cannot be significantly
> placed without comparative data on the morphology of the material it was
> related to. Caniniform teeth can be found in ornithischians in the
> maxilla, dentary, and premaxilla, and to assume that finding a canifiform
> and serrated conical crown and calling it a dentary tooth is preblematic.
> Caniniform teeth are found in pachycephalosaurians, heterodontosaurids,
> ceratopsians, and *Echinodon;* to which forms should the conical teeth of
> *Paronychodon,* often identified as pachy caniniforms, be identified if
> they are, indeed, ornithischians?

Which ornithischian forms have been named as such based on canine-like
teeth?  You're erecting a strawman here.  Paronychodon was named both a long
time ago, and as a plesiosaur.  Even IF it is an ornithischian (which is not
the current consensus), it hasn't been recently thought of as a valid genus
of that clade, so is irrelevent to your point.

> What theropod has the type's morphology
> to support referral on ziphodont crowns with lingual ridges to the genus
> hypodigm? That such teeth appear in varied taxa and conical teeth with
> additional ridges can appear in non-ornithischians in which the crowns are
> normally ziphodont (semi-heterodonty is known in tyrannosaurids and
> "ceratosaurs" _sensu lato_) reduces the quality of such diagnoses on their
> face; such caution in naming taxa on just teeth, or referring teeth to
> other tooth-taxa is questionable. Find a jaw, and this becomes easier to
> do; but without that jaw, it is a lot harder to do anything diagnostic or
> comparative with that tooth, based on the above reasons.

Again, arguing such a point with Paronychodon is useless.  The holotype is
lost, and people have been using it as a form genus for the past decade or
so.  I read a paper the other day with a great statement about how teeth are
not inherently worse for taxonomic purposes in dinosaurs than other elements
are.  If only I could remember the reference.  Some taxa have distinctive
teeth, some don't.  It's the same with other elements.  Dinosaurs jaws are
not realms of infinite variation, as you seem to believe.  We have enough
specimens to tell us what sort of variation is reasonable within a jaw.  If
something surprises us with newfound variability, and we named a couple taxa
based on the same taxon's incredibly heterodont teeth, oops.  Made a
mistake.  Oh well.  Could happen in most cases.  Megaraptor could have been
the same as Unenlagia, but they were still both named.  Marshosaurus could
have been Coelurus, but they were still both named.  If you're going to be
so conservative, only the best specimens would be named, reducing the
effectiveness of taxonomy.

>   The same is true for assuming an isolated centrum belongs to a
> particular portion of a caudal series, rather than another. Such an issue
> has been raised in the variable morphology of titanosaurian caudal
> vertebrae within a single specimen's series (unpublished material). If one
> wishes to argue this is restricted to titanosaurs, then the issue of the
> variability is just as arguable for any other taxon if it can appear in
> one, much less the variability of the shape of the centrum facets in
> sauropod tails within a series. I can apply the relative convexity of the
> cranial facet in *Spinosaurus* vertebrae as part fo a series which, as in
> *Baryonyx*, from increasing to decreasing convexity, as it appears to be
> true for all other tetanurans; if this is done, the length of the neural
> spine and its orientation are wildly varied in vertebrae for which the
> centra and neural arches are assuredly associated or fused (e.g., two
> consecutive vertebrae have neural spines almost at two orders of magnitude
> in length from one another, the anterior of the two shorter by almost half
> and oriented caudally, and the second oriented vertically, where more
> caudal vertebrae are cranially to caudally oriented -- the tallest neural
> arch appears to be a caudal dorsal spine, whereas centra associated or
> fused to neural spines of similar near-flattened centra show remarkably
> divergent and inconsistent spine shape and length).

Until I see it in a theropod, I'll assume such irregular variation in
central convexity is limited to sauropods.  More importantly however, there
are multiple factors that co-vary as one procedes down the vertebral column
in dinosaurs.  I have yet to see a taxon with a random arrangement of even a
few of these varying factors.
I can't see much of a point to the spinosaur example.  Only one of
Spinosaurus' neural arches was associated with a centrum, so any ordering of
arch characters in respect to central morphology is hypothetical.

> <They only vary in one character Sereno was able to find, which you have
> yet to defend the importance of.>
>
>   As may be clear yet, I am not trying to defend the distinctness of two
> taxa; rather, the distinction of identifying taxa based on the so-called
> applicability of distinct specimens based on similarity. The referral of
> Egyptian material Stromer referred to *Bahariasaurus* (but not comprising
> the type) to *Deltadromeus* does not preclude the applicability of the
> type Egyptian material to the Moroccan taxon. Rather, the argument I've
> been hearing is that the TYPE *Bahariasaurus* includes the referred
> material, and thus Sereno et al., 1996, are applying that *Bahariasaurus*
> is a nomen dubium based on so-called Egyptian *Deltadromeus* material.
> This has avoided that the diagnostic features of *Deltadromeus* that
> include the Egyptian material must therefore mean that the Egyptian and
> Moroccan taxa are synonymous. But this is subjective. Similarity can lead
> to lumping only as far as one can bend a line another uses to distinguish
> two taxa. Dissimilarity on any score can do the same thing. Aside from the
> tooth issue, the problem I have with saying *Deltadromeus* is
> *Bahariasaurus* is to make assumptions that the two taxa cannot be
> distinct; but this is not supportable on the given material. The latter is
> larger with differing morphology, which Sereno et al. selected from the
> hypodigm _similar_ material to their taxon as referrable. This was based
> on gross similarity, but not explicit character material. The same
> argument can be applied between (as it was in the 80's and early 90's)
> that *Velociraptor* included  *Deinonychus* and *Saurornitholestes,* but
> we can see where that argument has gone, as well. Perhaps a better
> appreciation of the subjectivity of phylogenetic work will lead to better
> analyses on some people's parts, but others seem to be aware of this
> already, and their work appears to reflect this very well.

The ICZN precludes the applicability of the type Egyptian material to the
Moroccan taxon.  If the two are the same, the Egyptian taxon must have
priority.
I've never argued the holotype of Bahariasaurus includes the referred
Egyptian "Deltadromeus" material, but rather that they are conspecific.
Note none of the "diagnostic features of *Deltadromeus* that include the
Egyptian material" can be determined to be absent in the Bahariasaurus
holotype.  Hence the assignment of the refferred Egyptian material to either
taxon would be baseless given the published data.
Sereno et al. were clearly not arguing that Bahariasaurus was a nomen
dubium, as they tried to differentiate it from Deltadromeus.
The two taxa COULD be distinct, but I see no evidence for it, and you've
presented none.  You keep saying they have differing morphology, but have
yet to say why you don't think they should be synonymized.  As I said
before, Carcharodontosaurus' holotype and referred skull SGM-Din 1 also have
differing morphology.  What if I erected Neocarcharodontosaurus based on
Sereno's Moroccan skull?  Would you support not synonymizing
Carcharodontosaurus and Neocarcharodontosaurus?  And if so, why?
BTW, Bahariasaurus is NOT larger than Deltadromeus, note the referred
Egyptian material of the latter is ~10% larger than Bahariasaurus' holotype.

> <You yourself stated the Baharija material was referrable to the same
> taxon as Deltadromeus yesterday, and both Sereno and I agree.>
>
>   I suggest what I wrote be read again; the typer was not referred, but
> was demoted as non-diagnostic. A few elements were referred, but did not
> comprise any portion of the type of *Bahariasaurus*. My statement on
> likely synonymy aside, this was, again, subjective, and based on an
> objective review (the goal of this post) I cannot refer any quality of
> synonymy when the data would not suggest there was a clear case OF
> synonymy, based on any lack of an alternate hypothesis. That the type for
> *Baharaijasaurus* includes material of a sufficient size to be distinct
> from *Deltadromeus* with a different set of elements known, makes the
> referral VERY subjective apart from hypodigmatic referral (and even that
> may be questionable, as the spacial and stratigraphical distance could
> imply a speciation variable that some authors provide sufficient to
> diagnose species [e.g., *Euronychodon* vs *Paronychodon*]).

I suggest you read what I wrote again as well.
I never said the Bahariasaurus type was referred to Deltadromeus.  Rather, I
was talking about the Baharija material Sereno et al. referred to
Deltadromeus (IPHG 1912 VIII; I thought the context made this clear), and
which you agreed to the referral.
Two points that were covered above-
- The holotype of Bahariasaurus was NOT believed to be undiagnostic by
Sereno et al., as they tried to differentiate it from Bahariasaurus.
- There is no great size difference between the Baharija material, both
holotype of Bahariasaurus and referred to Deltadromeus.
And as I've said before, the holotype of Bahariasaurus DOES SHARE comparable
material with the holotype of Deltadromeus.  They share parts of dorsal
vertebrae, pubis and ischium.
And as I've also said before, the spatial and stratigraphic separation does
not exist, as remains of both taxa are known from the Baharija Formation of
Egypt.

> <So since we all think Deltadromeus lived in the Baharija Formation
> alongside Bahariasaurus, there is no stratigraphic reason to consider them
> distinct.  There's no reason to consider Bahariasaurus a nomen dubium
> either, unless you can present another taxon (besides Deltadromeus) it
> can't be distinguished from.>
>
>   Since the type of *Bahariasaurus* decides the basis of a referral to a
> nomina valida or nomina dubia status, then one would have to show the
> material was diagnostic of a species, and that *Deltadromeus* shared all
> these features or a sufficient value of them. Rather, this is only
> predicated on a referred ischium (Sereno et al., 1996).

Don't know where reference to a referred ischium comes from.
I yet again ask you for another valid genus Bahariasaurus can't be
distinguished from, based only on the holotype.

> <No, the holotype of Carcharodontosaurus is a partial maxilla, teeth,
> nasal, parietal, cervical vertebrae, caudal vertebrae, manual ungual,
> ilium, pubis, femur and fibula.>
>
>   I do wonder what paper Mickey is reading. The type was distinguished as
> *Megalosaurus saharicus* by Deperét & Savornin in 1928 as an unumbered
> tooth in the collection of the MHNH; the referral of the partial skeleton
> from Baharija in 1931 by Stromer was specifically designated as a referral
> with distinction to the type tooth as bearing distinct features of the
> crowns (however, this is clearly improper, as the referred maxilla have
> perfectly bilaterally symetrical crowns, while the type crown shows a
> distinct recurvature with concave distal margin, as in the Moroccan skull
> (Sereno et al., 1996).

The paper I'm reading is Stromer 1931.  You can read it too-
http://blackwidow.informatics.sunysb.edu/anatsci/files/Stromer_31.doc
The holotype of Carcharodontosaurus is the partial skeleton I mentioned
(IPHG 1922 X46).  The holotype of saharicus is the two teeth, but you
specifically said "Actually, I would reject both skulls from
*Carcharodontosaurus* on the provision that the holotype is a tooth",
referring to the genus.

> <If we followed your advice, all bahariasaur material except the holotypes
> of the two taxa would be unassignable (including the Egyptian material you
> think is synonymous with Deltadromeus).>
>
>   As I said, I do not think they are synonymous. Just that I do not
> contradict nor think myself familiar enough to contradict or affirm their
> assignment. My work here is theoretical. Given the variable recovery apart
> from the holotypes and lack of articulation or association of nearly any
> element makes the taxonomic hypodigms questionable, and until better
> material can be found from Baharija to show the association of the
> referred material to the type, the absence of which cannot affirm
> Stromer's complex.

You DID think they were synonymous four days ago- "Portions of the hypodigm
that Stromer referred to *B. ingens* have been shown to belong to *D.
agilis*".  I dealt with your misunderstanding of comparable elements between
the types above.  Lack of association is not an issue here.
And though opting to stay theoretical may give you the advantage of not
"having to" present any further data on why the two taxa should stay
separate, your theoretical stance is flawed as well.

> <After all, who knows what the small amounts of variation indicate?>
>
>   All the reason to err on the side of caution than to start forming
> diagnoses and codings to employ loads of data from material that may or
> may not apply, as we are getting from the so-called properly associated
> *Patagosaurus* hypodigm. These days, when researchers in the Zuni basin
> are finding material like disassociated ceratopsian material, even if
> affirmed as a single taxon, only a single element is a type, and the
> apparent lack of referral of one "obvious" element, such as a squamosal
> that was an ischium, can change one's perspective of the hypodigm as a
> whole and to look more closely. This is also why the type of
> *Nedcolbertia*, depsite the complex of its hypodigm being found in a very
> small area, is a single bone.

I would think the "side of caution" here would be lumping rather than
splitting.  Better to assume a difference known to vary within a related
species is intraspecific than intergeneric.  And though mistakes like
Patagosaurus happen occasionally, we must recognize mistakes will occur
given realistic taxonomic philosophies.  The holotype of Nedcolbertia is the
entire partial associated skeleton of CEUM 5071, not a single bone (Kirkland
et al., 1998).

> <Indeed, all non-holotypic specimens of any fossil would be unassignable
> for the same reasons.>
> <Obviously, such reasoning doesn't work for other taxa, and we shouldn't
> use it as an excuse to erect a new taxon either.>
>
>   But such reasoning DOES work for other taxa. Note the *Ornithodesmus*
> argument. Or *Echinodon*, a little closer to home (at least for me).

Sorry, more explanation is needed.  How does your reasoning work for
Echinodon and Ornithodesmus?

Mickey Mortimer