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FW: Ichthyovenator



This doesn't seem to have made it to the list since I sent it 3 days ago. 
Resent.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

----------------------------------------
> From: qi_leong@hotmail.com
> To: archosauromorph2@hotmail.com
> Subject: RE: Ichthyovenator
> Date: Tue, 24 Apr 2012 04:47:21 -0600
>
>
>   Thanks to a DML reader for sending me the paper. I've had an opportunity to 
> read through the formal paper and the supplemental data.
>
>   Allain et al. justify their reference of sinusoidal as referring to a "two 
> humps" morphology with a concavity between, precisely as Brad notes for 
> *Concavenator corcovatus*. (The authors also use "sinusoidal" to refer to the 
> "S"-shaped flex/reflex curvature of the transverse processes of the caudals.) 
> This is justified on the basis of the morphology of the first sacral neural 
> spine (= neurapophysis) of MCCM-LH 6666, holotype of the new species. Allain 
> et al. note that the enter sacral block was found intact and associated as 
> described in the paper.
>
>   The first neural spine extends only half as high as the second, which is 
> 80% the height of the third, at which point the sacrum declines gradually to 
> the level of the caudal vertebral spines, which are intact and long. Allain 
> et al. aver that the spines are distal complete, thus not eroded or broken. 
> Their morphology is odd distally, but I will give Allain the benefit of the 
> doubt on this score. The sacral vertebral centra are not complete, and the 
> two preserved elements are identified as sv2 and sv3 by position relative to 
> the spines. They are found "fused" to one another, but have not coossified, 
> but the neural arches do not appear fused to the centra, implying a degree of 
> looseness not present in the holotype of *Spinosaurus aegyptiacus*.
>
>   Otherwise, the spines form a gradual arch with the distal end of sv1 at the 
> lowest point.
>
>   Allain et al. are sure the distal ends of the spines are intact and 
> unbroken. I am not sure, though, that they represent the natural distal ends, 
> although I cannot qualify this beyond the apparent incomplete morphology of 
> the last dorsal spine, and the morpghology of the complete, but distorted 
> penultimate dorsal spine, which is formed as a sagittal "T", distally 
> expanded anteriorly and posteriorly. I would presume that the succeeding 
> spine should bear similar morphology, as it does in other tall-spined 
> archosaurians. I cannot qualify my uneasiness when using clearly incomplete 
> material to justify curvature, especially since the life position of the 
> spines are being inferred from their _in situ_ relationships. One method to 
> resolve this is to use associated features of the spines, such as extents of 
> the pre- and postspinal laminae. However, these features are only apparent on 
> the dorsal vertebrae and caudal vertebrae; they are not described for the 
> sacrals, a result perhaps of the proximal irregular preservation, as there 
> are many cracks involved and the material may be slightly reconstructed (it 
> is not described in the text). The first sacral spine's distal extent only 
> extends as far dorsally as the position of the inferred continuation of the 
> interspinous ligament, which produces a distinct "spur" on the anterior and 
> posterior ends of the proximal spines of the dorsals, and the distal ends of 
> the caudal neural spines. This suggests that the spine may be more 
> continuous, but as Allain et al. argue, it is not distally broken.
>
>   I wonder, then, if the spines are incomplete otherwise due to ontogeny. The 
> surface appears irregular, rather than forming a smooth arch. Perhaps it was 
> encased in ligamental tissue. A similar feature occurs on the shallowest 
> sacral region in MCCM-LH 6666, holotype of *Concavenator corcovatus*. This 
> argument is not meant to dismiss the suggestion that the sacral region is 
> shallow between two "humps," but rather that such a feature may be incomplete 
> due to ontogeny. I otherwise have no basis for this argument, and the 
> features in MDS BK10 otherwise appear distinct from MCCM-LH 6666: the "gap" 
> or trough between "humps" is formed by a space of only two vertebrae, and the 
> authors presume that the second to last and last dorsals, and the third and 
> fourth sacrals were effectively the same height, and the second vertebra 
> nearly as high, placing the only disparity on the first sacral. I would then 
> presume that the problem here is that the first sacral spine is displaced in 
> the sample.
>
>   Note that none of this impacts the diagnosis Allain et al. argue for their 
> species, which is focused on the preserved pelvis and features of the dorsals 
> and caudals, rather than the sacrals. Pretty interesting nonetheless.
>
> Cheers,
>
> Jaime A. Headden
> The Bite Stuff (site v2)
> http://qilong.wordpress.com/
>
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>
>
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
> Backs)
>
>
> ----------------------------------------
> > Date: Tue, 24 Apr 2012 00:17:02 -0400
> > From: archosauromorph2@hotmail.com
> > To: dinosaur@usc.edu
> > Subject: RE: Ichthyovenator
> >
> >
> > "Sinusoidal" is the term used by Allain et al. I believe the intended 
> > meaning of it is that the sail that has an upswing, downswing, and then an 
> > upswing again.
> >
> > ----------------------------------------
> > > Date: Mon, 23 Apr 2012 11:16:34 -0600
> > > From: qi_leong@hotmail.com
> > > To: keesey@gmail.com; Brad.McFeeters@listproc.usc.edu
> > > Subject: RE: Ichthyovenator
> > >
> > >
> > > I'm not sure what is meant by "sinusoidal," but I'm sure that presuming 
> > > similarity to *Concavenator corcovatus* on the given description isn't 
> > > useful. "Sinusoidal" may instead refer to the shape of the sail as 
> > > presumed for *Spinosaurus aegyptiacus,* with a sharp anterior upswing, 
> > > followed by a gradual downswing in the profile.
> > >
> > > Cheers,
> > >
> > > Jaime A. Headden
> > > The Bite Stuff (site v2)
> > > http://qilong.wordpress.com/
> > >
> > > "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
> > >
> > >
> > > "Ever since man first left his cave and met a stranger with a
> > > different language and a new way of looking at things, the human race
> > > has had a dream: to kill him, so we don't have to learn his language or
> > > his new way of looking at things." --- Zapp Brannigan (Beast With a 
> > > Billion Backs)
> > >
> > >
> > > ----------------------------------------
> > > > Date: Mon, 23 Apr 2012 09:55:39 -0700
> > > > From: keesey@gmail.com
> > > > To: dinosaur@usc.edu
> > > > Subject: Re: Ichthyovenator
> > > >
> > > > On Sun, Apr 22, 2012 at 7:32 PM, Brad McFeeters
> > > > <archosauromorph2@hotmail.com> wrote:
> > > > >
> > > > > I have not read the paper yet, but I wonder if a sinusoidal sail 
> > > > > might actually be characteristic of female spinosaurids. Having a gap 
> > > > > in the sail above the pelvis might make it easier for the male to get 
> > > > > his leg over the female when mounting her (picture spinosaurids in 
> > > > > this position: http://www.luisrey.ndtilda.co.uk/html/carnsex.htm). A 
> > > > > somewhat similar condition is also seen in the type specimen of 
> > > > > Concavenator, maybe a solution to the same problem.
> > > >
> > > > Interesting idea! Possibly Becklespinax altispinax as well?
> > > >
> > > > Hopefully we have enough specimens to test this some day.
> > > > --
> > > > T. Michael Keesey
> > > > http://tmkeesey.net/
> > >
> >
>