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Re: Bahariasaurus & other questions



Dino Rampage wrote-

> 1) What is Bahariasaurus ingens? Is it a carnosaur closely related to the
> carcharodontosaurines (as was traditionally assumed) a basal tetanuran
with
> unknown affinities, or is it possibly a basal coelurosaur similar to
> Deltadromeus?

Synonymous with, or very closely related to, Deltadromeus.  Whether these
two are ceratosaurs (Carrano et al., 2002) or basal coelurosaurs is another
question.  Here's what I wrote in August regarding Bahariasaurus'
relationships, in my summary/review of Chure's thesis-
Bahariasaurus Stromer 1934
B. ingens Stromer 1934
Albian?-early Cenomanian, Early Cretaceous?-Late Cretaceous
Baharija Formation, Egypt; Continental Intercalaire, Niger?
Holotype- (HM 1922 X47) (11.9 m) dorsal vertebra (200 mm), dorsal vertebra
(~180 mm), neural arch, rib fragment, sacral vertebra (~135 mm), sacral
vertebra (~120 mm), sacral vertebra (~120 mm), pubes (1.03 m), proximal
ischium (Stromer 1934)
Referred- ? (HM 1911) caudal vertebrae, ischium
(HM 1912 VIII 82) ischia
? (MNNHN coll.) six caudal vertebrae (50-65 mm) (Lapparent 1960)
Comments- Chure finds this taxon to be closely related to tyrannosaurids
based on- nearly perpendicular expansion of glenoid margin of scapula from
blade; amphicoelous (non-opisthocoelous) anterior dorsal centra;
subtriangular obturator process; cranial tubercle on fibula; extremely
narrow scapular blade; longitudinal ridge on lateral surface of ischium.  I
disagree.
First, the scapula (HM 1912 VIII 60) is not part of the holotype, which
lacks pectoral material.  Also, tyrannosaurids do not have an expanded
glenoid margin (Carpenter and Smith, 2001) and their blade is much narrower
proximally, but expands distally (the opposite of this scapula).  The
expanded glenoid margin is present in such widely ranging theropods as
Compsognathus, Sinraptor and Baryonyx (Charig and Milner, 1997).  The last
taxon resembles this scapula very closely, differing only in that the
glenoid is more ventrally projected, the blade is a bit narrower distally
and the glenoid expansion is slightly stronger.  Oddly, that of Suchomimus
differs from these two in having a more prominant acromion, distally
expanded blade, and virtually no glenoid expansion, if the skeletal
reconstruction of Sereno et al. (1998) is accurate.  Perhaps the drawing is
inaccurate, or perhaps it belongs to Spinosaurus.  In any case, I refer this
scapula to the Spinosauridae.
The anterior dorsal vertebra (HM 1912 VIII 62b) is also a referred specimen
and non-opisthocoelous dorsals are also found in ceratosaurs,
"Szechuanosaurus" zigongensis and almost all coelurosaurs.  Tyrannosaurid
dorsals differ in being very short, with less waisted centra, wider neural
spines, narrower hyposphenes and taller neural canals (Maleev, 1974).  The
elongate centrum resembles some basal coelurosaurs (Compsognathus, SMNK 2349
PAL), so this vertebra may belong to Deltadromeus or Bahariasaurus.  Another
possibility is something like Elaphrosaurus, which may work with the
Deltadromeus identification too, if Longrich is right about it being more
basal than usually thought.
The triangular obturator process is not discernable in the holotype, but is
present in the complete juvenile(?) ischium HM 1912 VIII 82 that was
misidentified as a pubis by Stromer (1934).  Though much smaller than the
Bahariasaurus holotype, the morphology is nearly identical, differing only
in the less expanded anteroventral corner of the pubic peduncle.  I thus
feel it is properly referred to Bahariasaurus, and it is interesting that it
differs from the distal ischium of Deltadromeus (pubis in Sereno et al.
1996) only in that the boot is less extensive posteriorly, a probable
juvenile trait.  The obturator process is indeed triangular, but this is
known in nearly all coelurosaurs (except Sinosauropteryx and SMNK 2349 PAL),
not just tyrannosaurids.  Though the morphology of the boot resembles
abelisauroids more than any coelurosaur, the obturator morphology firmy
places it in the latter clade.  The presence of an ischial boot and the
proximal placement of the obturator process excludes Bahariasaurus from the
Maniraptora.  It differs from tyrannosauroids in lacking a proximolateral
scar or proximodorsal process, and having a distal boot and more prominent
ilial peduncle.  The lateral ridge on Bahariasaurus is caused by distortion,
as Chure himself says earlier in the thesis.  Where exactly Bahariasaurus
and Deltadromeus belong in the basal Coelurosauria may be revealed by my in
progress analysis.
The fibula is another referred specimen (HM 1912 VIII 70), this one later
referred to Deltadromeus by Sereno et al. (1996).  I agree as it is nearly
identical.  The anteriorly placed iliofibularis tubercle is primitive for
theropods (Rauhut, 2000), so does not indicate tyrannosauroid affinities in
Deltadromeus either.
Rauhut (1995) referred Bahariasaurus to the Allosauroidea based on the
distally reduced pubic symphysis (also in SMNK 2349 PAL), obturator notch
(plesiomorphic for avetheropods), quadrangular obturator process (not
present in Bahariasaurus), and "shape and height" of the anterior trochanter
(plesiomorphic for coelurosaurs).  He placed it in the Carcharodontosauridae
based on the presence of caudal pleurocoels, but this based on a referred
specimen (HM 1912 VIII 62b) whose relationship to Bahariasaurus is
uncertain.  I therefore reject Rauhut's hypothesis Bahariasaurus is a
carcharodontosaurid or an allosauroid.
Bahariasaurus is considered a nomen dubium by Chure, but it can be
distinguished from all comparable theropods except Deltadromeus, with which
it is probably synonymous.  Sereno et al. distinguished the two by three
characters, two of which were due to his misidentification of the distal
pubis as an ischium.  The other is the narrower ilial peduncle of
Bahariasaurus' ischium.  I doubt the importance of this character,
considering the temporal and stratigraphic proximity of the taxa.

> 4) Have the two new species of ceratopsid (one centrosaurine, one
> chasmosaurine) from the Lower Campanian been described & named yet?

If you're referring to the ceratopsid from the Wahweap Formation, shown by
Smith and Sampson at SVP 2002, it's still undescribed.

> 5) Are Zuniceratops & Avaceratops considered true ceratopsids or merely
> basal coronosaurs?

Zuniceratops is basal to ceratopsids, but Avaceratops is controversial.
Penkalski and Dodson (1999) placed it outside Ceratopsidae, but Forster
(2002) placed it in Centrosaurinae.

In response to Nick Gardner's questions-

> -Superior temporal fenestra merge above the temporals
> I don't really understand this character as when I look at the skull of
> tyrannosaurids in dorsal view, they do not appear to merge, but they are
> very close together.  Perhaps the translator made an error.

It means the supratemporal fossae merge to form a sagittal crest on the
parietal.  Of course, cranial material is unknown for Bahariasaurus, so this
is in reference to Carcharodontosaurus.

> -Centrally located neural processes in the caudal vertebrae
> I presume he's talking about the neural arches, but aren't these always
> located centrally?

Probably the neural spines, which appear to be posteriorly located in
Allosaurus because the anterior spur is separated from the main (posterior)
part of the spine by a dorsal concavity, making the spine appear to be
placed posteriorly if you only include the posterior part.  Even Rauhut
(2000) made this mistake.

> -Acromial region of the scapula extremely wide
> Evidentally, the scapula (HM 1912 VIII 60) was referred away from B., so
> this character cannot be used.  I presume it was referred to Deltadromeus,
> because the figures in SERENO et al 1996 illustrate D. with this
character.

HM 1912 VIII 60 is not referrable to Deltadromeus, though Deltadromeus does
indeed show this character.

> -Zygomatic process
> Could someone clarify on this character?

Confusing.  It would traditionally refer to a jugal process, but I don't
know any processes in Acrocanthosaurus that tyrannosaurids have and
allosaurids lack.

> -Wide postorbital edge
> Which edge?

The ventral process.

> -Mature pleurocoels on the posterior dorsal vertebrae
> Dorsal pleurocoels are present in at least Yanornis, Changchengornis,
> Confuciusornis, Deinonychus, Eoalulavis, Hesperornis, Ichthyornis,
> Longchengornis, Neuqueornis, Nomingia, Oviraptorids, Protopteryx,
Rahonavis,
> Saurornitholestes, Cathayornis, the Spanish nestling, Nanshiungosaurus?
> brevispinus, Beipiaosaurus, Microvenator, tyrannosaurids, Caudipteryx,
and
> possibly Archaeopteryx.  They should be present in more taxa, but I'm not
> certain which.

The lateral fossae in most basal birds (Confuciusornis, Changchengornis,
Longchengornis, Protopteryx, Sinornis (=Cathayornis), Eoalulavis, Yanornis,
Ichthyornis) are not described well enough to tell if there were pleurocoels
inside.  Neuquenornis seems to just have lateral grooves.  Deinonychus,
Archaeopteryx and Rahonavis all have lateral fossae with pleurocoels inside.
I don't think Hesperornis has lateral fossae or pleurocoels.  I've also
never heard of a description of the condition in the Catalan nestling.
Nanshiungosaurus brevispinus (which is the type species) has anterior
pleurocoels, but no posterior pleurocoels.  Beipiaosaurus has lateral fossae
in some posterior dorsals, though Xu et al. (1999) code these as
pleurocoels.  Caudipteryx is said to lack "deep pleurocoels" (Zhou et al.,
2000) and one dorsal is said to lack "noticeable pleurocoels" (Zhou and
Wang, 2000).

Mickey Mortimer