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



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. 
>