[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)

1. I'm not concerned that there's two sets of associated partial limb
bones and vertebrae in two different formations 3500 miles apart from
one another. This is a coincidence, and little more. My concern over
how they were associated is a bit more of a concern. Supposedly, only
some of the limbs and a few other bits were discovered of what is now
FSAC-KK 11888 actually associated in the discovery locality, whereas
much of the vertebrae, and quite possibly the vertebrae in question
may have been recovered elsewhen. If this is so, and we don't have the
locality info for all pieces and their collection times, we have
limited basis to argue that the two sets of limbs are even
coincidentally associated with similar proportions to vertebrae they
were collected with ... because they may not have been collected with

More important then becomes the question of where we find disparate
sizes amongst vertebrae and almost no limb bones in these spinosaur
skeletons, but more readily their teeth, vertebrae, etc. For
vertebrae, the answer may be density, whereas for teeth it's
plentitude. We have a higher chance of recovering denser, and more
common, material, than we have lighter and rarer material.

So my issue with the agreement in general proportions between the
tibiae/dorsal proportions is that we've no rational basis to assume
they are properly associated _at all_. Collected, adjacent, whatever,
based on anecdotes. I am cautious about anecdotes in material

2. Funny fact: I just scrapped a paper due to this one that I was
writing in my attempt to explain association and likely arrangement of
*Spinosaurus aegyptiacus* vertebrae, based solely on the description
from Stromer and my own observation. In it, I found a similar
reasoning for there being two distinct morphs in _each_ formation. It
was one of the conclusions I'd had that Evers et al. made for me, and
I'm happy now to see it in print.

Little known is the nature of the north African region during and just
before the Cenomanian. At this time, transgressions from the north and
south divided west Africa from the bulk of the continent, and at one
point during the early Cenomanian may have completely divided but for
a thin land bridge west from east. This is speculative, because almost
all faunal data on this division is based on the aquatic fauna;
limited info has been made on the terrestrial faunae between east and
west, with general conclusions (all cited in Evers et al.) suggesting
that while similar, there are nonetheless taxonomic differences
between them. Some taxa occur in both sides that are very, very
similar, but still distinct. So much so, we might predict that those
elements that are missing from either might be present.

Evers et al. made me ditch a paper in which I would have used faunal
similarity and taxic dissimilarity as an argument against subsuming
all taxa in either side of this potential land bridge into just one.
And I'm pretty happy about that. They made the point more concisely
than I tend to.

3. Ultimately, I'm okay with subsuming taxa, should there be no
justifiable reason to recognize distinction. I'm just conservative in
my approach. I have as much concern over the plethora of Nanxiong Fm
oviraptorids as you do, and have even published comments on my blog
with the concern over potential synonymies. You've probably read them.
But limited data is limited, and that means we should withhold broad
statements on referral and rejection of taxonomy because of them.

On Thu, Oct 22, 2015 at 1:27 AM, Mickey Mortimer
<mickey_mortimer111@msn.com> wrote:
> Ibrahim et al. were wrong to call the pectoral vertebra in figure S2 neotype 
> material.  I agree with Evers et al. there.  I bet it's actually based on 
> isolated pectorals MSNM V6874, V6877 or V7143 that they list as new.  The 
> comparison they made was of Sigilmassasaurus to Spinosaurus B (pectoral 
> verts), then Spinosaurus B to the neotype (limbs and caudals), then the 
> neotype to the holotype (dorsals).  Now if you doubt Spinosaurus B and/or the 
> neotype are properly associated (like Evers et al. do), then that breaks 
> down, but you still have to explain the convenient small and similar 
> hindlimbs and large similar vertebrae plus weird distal caudals in both.
> And yes, we disagree on taxonomic principles.  I knew you'd like the paper 
> when I was reading it.
> An interesting aspect of Evers et al. is that they describe non-brevicollis 
> morph vertebrae from Morocco too, including those in the neotype.  Which 
> matches Hendrickx's (2006) thesis showing two morphs of spinosaurine Moroccan 
> quadrates.  Similarly, they agree Egyptian Spinosaurus B as has the 
> brevicollis morph, unlike the aegyptiacus holotype from that country.  So if 
> we have different species, it wasn't just an East vs. West thing.  I think 
> their dual species hypothesis is quite plausible, but not only is it messy 
> for non-presacral remains, we have such a small sample size of associated 
> specimens (3), and the only one still existing hasn't been described well 
> yet.  So I'm Waiting For The Paper, as Holtz says, before reconfiguring 
> African spinosaurine taxonomy.
> Mickey Mortimer
> ----------------------------------------
>> Date: Wed, 21 Oct 2015 12:13:16 -0700
>> From: jaimeheadden@gmail.com
>> To: mickey_mortimer111@msn.com
>> CC: dinosaur@usc.edu
>> Subject: 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 a
>> "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 wa
>> 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 f
> r 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
>>>> 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
>>>> 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
>>>>> 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)

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

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