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

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 lived in the "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 in limbbone 
morphology (for which there is 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
> To: dinosaur@usc.edu
> Subject: Sigilmassasaurus (theropod) redescribed with new material (free pdf)
> Ben Creisler
> 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 found to be more widespread
> 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.