Spinostropheus gautieri identified as an ... alvare.. wait a second!

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

Tim Williams wrote-

> BTW, the ceratosaurian affinities of _Spinostropheus_/_Elaphrosaurus
> gautieri_ replaces an early suggestion for this African theropod's
> affinities:
>
> http://www.cmnh.org/dinoarch/2002Jul/msg00370.html
>
> [Sorry Mickey - hope this post doesn't come back to haunt you.   :-)  ]

I based my identification on five characters.  Three (procoelous caudal
centra, ventral median keel on caudal centra, short humerus) are not
mentioned by Sereno et al. (2004) at all.  Sereno et al. illustrate
Spinostropheus with amphicoelous cervical centra, though Lapparent described
them as opisthocoelous.  Though Lapparent's figure can be interpreted as
opisthocoelous, it could also be interpreted as amphi/platycoelous if it has
the oddly angled anterior surface of Spinostropheus.  Strangely, Sereno et
al. code Spinostropheus has having markedly opisthocoelous postatlantal
cervical centra, agreeing with Lapparent, but not their own figure.  It's
all moot however, as this would work well with Spinostropheus being a
ceratosaur or derived alvarezsaurid.  Finally, Sereno et al. illustrate the
fifth dorsal as having a normal-sized neural canal (<25% of central height),
not the greatly enlarged (>52%) one described and illustrated by Lapparent.
This can vary throughout the series in other theropods (eg. Deinonychus),
but the anterior canals are largest, so I think this much variation between
anterior dorsals is unrealistic.  Lapparent's photo would be an odd
morphology for a theropod dorsal vertebra, however.  One distinct possiblity
is that not all of these remains came from the same taxon.  There is no
indication Lapparent's first set of material (cervical vertebra, three
dorsal vertebrae, four dorsal fragments, three sacral fragments, three
caudal vertebrae, two caudal fragments, partial humerus, ulna, distal pubis,
distal femur, incomplete tibia, incomplete fibula, proximal metatarsal, four
metatarsal fragments, partial pedal phalanx) was associated.  Indeed, the
ulna was stated to be isolated, and the proximal metatarsal comes from a
different locality.  His second set of remains (cervical neural arch, two
dorsal vertebrae, sacrum, partial caudal vertebra, three manual unguals,
tibiae, distal fibula, proximal metatarsal, four pedal phalangeal fragments)
apparently come from a single individual.  While this could allow the
referral of some of the first set of remains to the same taxon, if the first
set was completely disassociated, the humerus, ulna, pubis, femur and
metatarsal fragments would have no reason to be referred.  Sereno et al.
only include unspecified vertebrae, a partial humerus and partial tibia in
the holotype of Spinostropheus.  Incidentally, Lapparent did not designate a
holotype, so Sereno et al. are the first to do such for the taxon as far as
I know.  Perhaps they did further resrarch to discover the pubis, femur,
fibula and pedal elements were not associated with the rest of the first set
of remains?  Sereno et al.'s opinion on Lapparent's second set of remains is
unknown.  They only code Spinostropheus based on their new material, which
is unhelpful in determining their thoughts on Lapparent's material.  I'll
have to e-mail Sereno to find out what the situation is, and will report
back what I discover.  Incidentally, I have no problem with the new specimen
and its homologs in Lapparent's material (the cervical photographed looks
similar, at least) being ceratosaurian.

But hey, at least he finally placed new material into an old poorly known
taxon, instead of nomen-dubiafying it and naming a new genus. :-)

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