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

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Jaime Headden wrote-

>   De Lapparent (1960) illustrated a "caudal" (Plate V, fig. 5) as a
> portion of his diagnosis, but it is almost painfully obvious that this is
> a dorsal vertebra as the transverse processes are horizontal and well
> above the centrum both anteriorly and caudally, without any suggestion of
> a parapophysis on the centrum, as in *Spinostropheus,* as well as any
> pleurocoel as in the cervicals. Its length and shape agrees with the
> dorsals of *Spinostropheus,* rather.

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.

> The tibia exhibits
> the "typical" ceratosaurian astragalar articulation, where a fold of the
> tibia encompasses the medial edge of the ascending process, as in
> *Elaphrosaurus* (though much more weakly).

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

>   *Spinostropheus* shares some features with *Elaphrosaurus,* including
> elongated, low neural spines of the cervicals and dorsals, and epipophyes
> broader than deep and largely oriented horizontally. This could affirm
> this taxon as the first true inclusive representative of a monophyletic,
> multi-taxon "elaphrosaurid" basal abelisaurian clade.

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.
- Postaxial presacral vertebrae, posterior pleurocoel, form: partially
sharp-rimmed and invaginated.
- Mid dorsal parapophyses, form: process with cylindrical shaft.
- Cervical epipophyses, form: mid cervical epipophyses anteroposteriorly
extended with anterior corner
- Cervical epipophyseal-prezygapophyseal ridge/lamina, form and
distribution: prominent crest or lamina in
all postaxial cervicals.
- Mid cervical (C4-8) ribs, lateral process for articulation with successive
rib spine: present.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html