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Re: Sigilmassasaurus (theropod) redescribed with new material (free pdf)



" It also wouldn't change Ibrahim et al.'s taxonomic conclusion- that
Spinosaurus B and thus Sigilmassasaurus are both Spinosaurus."

No, that one depends on there having been evidence to support making a
proposition. Ibrahim et al. offered none. Instead, Ibrahim wrote:

"One or more of the characteristic cervicodorsal vertebrae attributed
to this taxon are now known in associated specimens in several
spinosaurids including “Spinosaurus B” and probably Baryonyx and
Suchomimus. In the latter two genera, the cervicodorsal vertebrae of
interest are somewhat fragmented (Baryonyx) or not completely exposed
(Suchomimus), although both seem to show many of the suite of features
that characterize these cervicodorsal vertebrae. These include a very
low and broad centrum, strong opisthocoely, small pleurocoels, a
prominent ventral keel, strong transverse processes, and broad
zygapophyseal facets with very low epipophyses. There is no
justification for the differentiation of this taxon from S.
aegyptiacus."
(supp. info, pg 11)

Basically, they say nothing specifically about the type of
Sigilmassasaurus brevicollis compared to Spinosaurus aegyptiacus.
Instead, they inferred similarity to "Spinosaurus B" (agreeing with
McFeeters et al. 2013) but concluded that SB was aegyptiacus without
any further overlap. Then they generalized spinosaur characteristic
with reference to completely different, and baryonychine, taxa. No
actual evidence is used to compare SB to Sigilmassasaurus brevicollis,
and the SB->Spinosaurus comparison is based on assumed proper
association of FSAC-KK 11888, which is - to be blunt - an issue of
begging the question.

No actual comparison was done. They assume them to be synonymous. And
the reason is made clear in Evers et al., and by the curious omission
in Ibrahim et al., by the improper comparison in their Supplemental
Figure S2 (pg 23) in which a cervical of SB is compared to an apparent
cervical of FSAC-KK 11888, deemed "neotype material", that doesn't
apparently exist, but matches that of their artificial model, thus
that it is comprised of a sculpted, and artificial vertebra. The
additional curiosity then shows how their argument becomes further
circular when you consider how the artificial model was produced by
collating SB, aegyptiacus, maroccanus, and FSAC-KK material. So of
course, it will compare well. If you compare a thing to a slightly
modifed form of itself, they will agree rather well, like comparing
the average to the mean. Differences be damned.

I err on the side of original taxonomic assignment. It represents the
base position further taxonomic work should be built upon, or from
which a case against must depend. Thus, I question Ibrahim et al.'s
taxonomy; Russell's predates it, and is the firmer of the two.
Cristatusaurus is probably the same thing as Suchomimus, but until
description of the latter comes forth, we cannot confirm nor deny
this, but it seems pretty good based at least on the premaxilla they
may represent the same taxon, albeit at different sizes. I don't
predicate taxonomy on the basis of lumping or splitting, as this issue
was raised before, because both positions require evidence from the
base argument to work from. Similarly, if someone names out a specimen
of the *Archaeopteryx lithographica* complex that has been a part of
the thing for decades (*Wellnhoferia grandis*) then that bears more
scrutiny than when a specimen is first named as something else before
referral to *Archaeopteryx lithographica* (*Archaeornis siemensii*,
*Archaeopteryx recurva*).

...

The fact is, there are differences between the eastern and western
specimens. These differences support the inference for more than one
taxon. Whether a single taxon crossed the epicontinental seas that
covered portions of northern Africa from the north or south is an
issue for biostratigraphy and geology. As it is, as Evers et al.
write, there are distinct taxonomic groups on either side that have
firmly been accepted, despite being similar to one another; they are
not the same things.

On Wed, Oct 21, 2015 at 1:58 AM, Mickey Mortimer
<mickey_mortimer111@msn.com> wrote:
> It's Mickey, please.
>
> The mismatched axial vs. appendicular size in the neotype is evidence for its 
> correct association because we have the same situation in Spinosaurus B.  
> It's possible we coincidentally got these associations twice with a large 
> spinosaurid and small whatever-the-hindlimb-is in both Egypt and Morocco, but 
> that seems unlikely.  As for the 'year class idea', so the older individual 
> in both cases just
>  happened to preserve only vertebrae while the younger individual only
> preserved the hindlimb?  Again, that would be a coincidence.  It also 
> wouldn't change Ibrahim et al.'s taxonomic conclusion- that Spinosaurus B and 
> thus Sigilmassasaurus are both Spinosaurus.  On the other hand, Rauhut's 
> (2000, 2003) questioning of Spinosaurus' holotype being one taxon was done 
> before we had the neotype or the new Ichthyovenator specimens, both of which 
> show spinosaurine teeth associated with tall dorsal neural spines.  Sure you 
> can doubt one, or maybe two, but doubting all three is really pushing it.  
> But yes, I'm all for waiting on the description of the neotype for a better 
> conclusion.  Still, Ibrahim et al.'s general idea of Spinosaurus' holotype 
> and neotype, Spinosaurus B and Sigilmassasaurus all being the same kind of 
> thing, regardless of how many species are involved, would explain these 
> apparent coincidences.
>
> Mickey Mortimer
>
> ________________________________
>> Date: Wed, 21 Oct 2015 00:15:40 -0700
>> Subject: RE: Sigilmassasaurus (theropod) redescribed with new material
>> (free pdf)
>> From: jaimeheadden@gmail.com
>> To: mickey_mortimer111@msn.com
>> CC: dinosaur@usc.edu
>>
>>
>> Michael, as you yourself note, we have little information as to how and
>> in what arrangement the material collected at either Egyptian or
>> Moroccan locality were. Arguing as Ibrahim et al did that the
>> arrangement of vertebrae to limbs, and the mismatched size between the
>> two, were evidence for their rightness in associating the Moroccan
>> material, despite its disparate collection process, but at the same
>>
>> collection in the *Spinosaurus aegyptiacus* holotype, sounds like
>> you're missing most of the point.
>>
>> Evers et al are also noting the problems of association. They do so for
>> all sets of specimens involved. Their authorship includes Rauhut, who
>> made the strongest published case for polytaxic assemblage in that
>> holotype. Their arguments concern themselves primarily with vertebrae,
>> and secondarily with vertebrae associated with other material. They are
>> skeptical of association in FSAC-KK and in the BSPG material, not just
>> the one. They don't care that the verge in both are seemingly much
>> larger, they merely note that proportional differences between the two
>> sets, morphological differences between them and the different
>> directions they point in even were they considered monotaxic specimens.
>> The assumption is that high disparity in apparent age in either
>> specimen should be met with concern, not ways to confirm association.
>> Ibrahim et al should not have, in this person's opinion, assumed the
>> association was authentic. Indeed, it might merely be consistent
>> association across year classes -- and nothing more. That would be more
>> interesting, radical, than what they ended up arguing. And which I
>> might add, they've begun walking back. I think we should at the least
>> wait until Ibrahim and Allain publish their respective papers. I say so
>> on my blog, which also references your comment here, in part.
>>
>> https://qilong.wordpress.com/2015/10/20/pale-spinos-sigilmassasaurus
>>
>> On Oct 20, 2015 6:49 PM, "Mickey Mortimer"
>> <mickey_mortimer111@msn.com<mailto:mickey_mortimer111@msn.com>> wrote:
>> There's a lot of great information in the paper, including new
>> positional assignments for Baryonyx's presacral vertebrae.  But I think
>> MUCH is made of the differences between African spinosaurine specimens
>> while seemingly little effort went into checking for similarities.  I
>> wouldn't be surprised if multiple species of spinosaurines l
>
>> "Mid" Cretaceous of North Africa, and some of the differences noted by
>> Evers et al. and the studies they cite seem to support that.  Yet Evers
>> et al. don't support or even suggest that any of the material is more
>> closely related to another spinosaurine.  So why can't it all be
>> Spinosaurus?  And if it's all Spinosaurus, why not all S. aegyptiacus?
>> It becomes a lumper-splitter issue at that point, and I'll note if
>> Evers et al.'s taxonomy is used (Sigilmassasaurus brevicollis, S. sp.
>> for 'Spinosaurus B', Spinosaurus aegyptiacus for the holotype only),
>> then virtually all African spinosaur materials are Spinosauridae/-inae
>> indet..  So muc
>>   h like the situation for other theropods (e.g. Allosaurus,
>> Microraptor, Archaeopteryx) where we either have every
>> individual/quarry be a new species or else have one morphologically
>> variable species, I'm sticking with the latter for pragmatic/utility
>> concerns if nothing else.  At least until the S. aegyptiacus neotype is
>> described fully.  Based on Rauhut's 2014 SVP abstract, I think he has a
>> different taxonomic mentality than I do though, with 3-5 species of
>> Archaeopteryx and each Compsognathus specimen being a separate species.
>>
>> Finally, the approach Evers et al. take is extremely skeptical.  The
>> Spinosaurus B vertebrae might not go with the hindlimbs, its caudals
>> might not go with either, it's similar to Sigilmassasaurus but can't be
>> demonstrated to be the same species, the neotype is completely
>> untrustworthy, and even the association of Spinosaurus' holotype isn't
>> taken for granted.  Sure technically these things aren't proven, but
>> there would have to be some unlikely coincidences otherwise.  The small
>> hindlimbs with large vertebrae in bot
>>   being found with both, and in Ichthyovenator, and in the same
>> formation as Oxalaia, etc..  As they say, "unless one assumes that
>> these specimens represent closely related taxa with very similar
>> proportions, but differences
>
>> no independent evidence), this coincidence in proportions is of
>> doubtful value to prove association."  Well yes, that's exactly what I
>> "assume".
>>
>> Mickey Mortimer
>>
>> ----------------------------------------
>> > Date: Tue, 20 Oct 2015 08:30:27 -0700
>> > From: bcreisler@gmail.com<mailto:bcreisler@gmail.com>
>> > To: dinosaur@usc.edu<mailto:dinosaur@usc.edu>
>> > Subject: Sigilmassasaurus (theropod) redescribed with new material
>> (free pdf)
>> >
>> > Ben Creisler
>> > bcreisler@gmail.com<mailto:bcreisler@gmail.com>
>> >
>> >
>> > New in PeerJ:
>> >
>> > Serjoscha W. Evers, Oliver W.M. Rauhut, Angela C. Milner, Bradley
>> > McFeeters & Ronan Allain (2015)
>> > A reappraisal of the morphology and systematic position of the
>> > theropod dinosaur Sigilmassasaurus from the “middle” Cretaceous of
>> > Morocco.
>> > PeerJ 3:e1323
>> > doi: https://dx.doi.org/10.7717/peerj.1323
>> > https://peerj.com/articles/1323/
>> >
>> >
>> >
>> > Sigilmassasaurus brevicollis is an enigmatic theropod dinosaur from
>> > the early Late Cretaceous (Cenomanian) of Morocco, originally based on
>> > a few isolated cervical vertebrae. Ever since its original
>> > description, both its taxonomic validity and systematic affinities
>> > were contentious. Originally considered to represent its own family,
>> > Sigilmassasauridae, the genus has variously been suggested to
>> > represent a carcharodontosaurid, an ornithischian, and, more recently,
>> > a spinosaurid. Here we describe new remains referrable to this taxon
>> > and re-evaluate its taxonomic status and systematic affinities. Based
>> > on the new remains, a re-evaluation of the original materials, and
>> > comparisons with other spinosaurids, the holotype of Sigilmassasaurus
>> > brevicollis is identified as an anterior dorsal, rather than a
>> > cervical vertebra, and differences between elements referred to this
>> > taxon can be explained by different positions of the elements in
>> > question within the verteb
>> > to diagnose the genus and species are fo
>> > among basal tetanurans, and specifically spinosaurids. However, the
>> > taxon shows several autapomorphies that support its validity,
>> > including the presence of a strongly rugose, ventrally offset
>> > triangular platform that is confluent with a ventral keel anteriorly
>> > in the mid-cervical vertebral centra and a strongly reduced lateral
>> > neural arch lamination, with no or an incomplete distinction between
>> > anterior and posterior centrodiapophyseal laminae in the posterior
>> > cervical and anterior dorsal vertebrae. We argue furthermore that
>> > Spinosaurus maroccanus, also described on the basis of isolated
>> > cervical vertebrae from the same stratigraphic unit and in the same
>> > paper as Sigilmassasaurus brevicollis, is a subjective synonym of the
>> > latter. Both a detailed comparison of this taxon with other theropods
>> > and a formal phylogenetic analysis support spinosaurid affintities for
>> > Sigilmassasaurus. However, we reject the recently proposed synonymy of
>> > both Spinosaurus maroccanus and Sigilmassasurus brevicollis with
>> > Spinosaurus aegyptiacus from the Cenomanian of Egypt, as there are
>> > clear differences between the vertebrae of these taxa, and they do not
>> > share any derived character that is not found in other spinosaurids.
>> > Together with a comparison with other spinosaurid vertebral material
>> > from the Kem Kem, this suggests that more than one taxon of
>> > spinosaurid was present in the Kem Kem assemblage of Morocco, so the
>> > referral of non-overlapping material from this unit to a single taxon
>> > should be regarded with caution.
>>
>



-- 
Jaime A. Headden
The Bite Stuff: http://qilong.wordpress.com/


"Innocent, unbiased observation is a myth" - P. B. Medawar (1969)