Re: *Spinostropheus* Replaces "Elaphrosaurus," a Possible "Elaphrosaurid"

["Jaime A. Headden" <qilongia@yahoo.com>]

Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:
 
<I disagree.  The specimen appears to be a caudal centrum, as originally
described.  The centrum is more elongate than any dorsal of Spinostropheus
and extends anterior to the neural arch far more.  Transverse processes in
identical position are noted in some Elaphrosaurus caudals (Janensch,
plate IV, fig. 4).  And of course, it's procoelous, unlike Spinostropheus'
dorsals which have concave anterior articulations.>

  This would make the mid-dorsals in *Spinostropheus* procoelic as well,
and therefore both specimens are amphicoelous with concave cranial and
caudal articulations. Yes, in *Elaphrosaurus,* transverse processes are
above the neurocentral suture, so that's not a particularly key diagnosing
feature. Centra in caudal dorsals become progressively elongate in
*Spinostropheus,* so it is not unlikely the element is a dorsal because of
its length:height, though it may come from an older animal, depending on
the relative length:height factor.

<I don't think this can be determined from the photograph.>

  I can determine some things, but this is true, and is true even for
*Elaphrosaurus,* where the astragalar fossa is indistinct apart from the
"folding" edge. A feature on the distal tibia would correspond to this,
and was commented upon by de Lapparent.

<Perhaps, but then you'd have to explain the characters shared by
Spinostropheus and abelisaurians, and those shared by those two taxa and
ceratosaurids, to the exclusion of Elaphrosaurus.>

  Mickey clarified to me privately that this list is taken from the
analysis in the paper, not from observations, so errors are not his but
relate most likely to the ACCTRAN distribution of characters applied to
nodes.

<- Postaxial presacral vertebrae, posterior pleurocoel, form: partially
sharp-rimmed and invaginated.>

  Present in median to posterior cervicals in *Elaphrosaurus.*

<- Mid dorsal parapophyses, form: process with cylindrical shaft.>

  Present in *Elaphrosaurus* as well as all Abelisauria, as a diagnostic
feature in dorsals where known; the only difference is the lack of a
lamina connecting para- and diapophyses in *Spinostropheus,* as I noted in
my post.

<- Cervical epipophyses, form: mid cervical epipophyses anteroposteriorly
extended with anterior corner>

  Absent in non-abelisauroids (*Noasaurus* + *Carnotaurus*); not present
in *Chuandongcoelurus,* *Ligabueino* (another likely "elaphrosaurid"),
*Elaphrosaurus,* or *Spinostropheus.*

<- Cervical epipophyseal-prezygapophyseal ridge/lamina, form and
distribution: prominent crest or lamina in all postaxial cervicals.>

  It can be said that *Elaphrosaurus* has very slender vertebrae, very
highy arches, and highly modified.

<- Mid cervical (C4-8) ribs, lateral process for articulation with
successive rib spine: present.>

  Since no cervical ribs in *Elaphrosaurus* are well preserved, or
complete much beyond a centimeter or two of their length, this is not
determinable.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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


        
                
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