[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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

Hooray for the snip glitch!  The fourth sentence in the second paragraph should 
read- "The small hindlimbs with large vertebrae in both Spinosaurus B and
 the neotype, the same kind of caudals being found with both, and in 
Ichthyovenator, and in the same formation as Oxalaia, etc.."

Mickey Mortimer

> Date: Tue, 20 Oct 2015 18:49:22 -0700
> From: mickey_mortimer111@msn.com
> To: dinosaur@usc.edu
> Subject: 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 m
> 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
> 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 carcharodon
>> 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 as

>> referral of non-overlapping material from this unit to a single taxon
>> should be regarded with caution.