Re: Some Comments on *Bahariasaurus ingens* Stromer (1934)

["Jaime Headden" <ja_headden@qilong.8m.com>]

Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:

<1912 VIII 81 does not seem to be Bahariasaurus.  The two differ in several
ways.  Bahariasaurus has a less conspicuous and more proximally placed lateral
flaring (15% down the shaft, compared to 21%).  The distal end is
not flared laterally.  There is an extensive separation of the pubic shafts
distally, and the interpubic foramen is more distally placed (80% down the
shaft, vs. 71%).
  Also, the pubis of Deltadromeus' holotype seems to be an ischium.  Note the
shape of the distal boot is almost identical to 1912 VIII 82, except that it's a
bit shorter in the latter (possibly ontogenetic, as seen in Nedcolbertia).  The
lack of an interpubic foramen in Deltadromeus' "pubis" (again similar to 1912
VIII 82) is also consistant with an identification as an ischium, though plenty
of taxa lack interpubic foramina.  Finally, this would explain the narrowness of
Deltadromeus' "pubis".  The pubes in Deltadromeus are far too incomplete
proximally to judge apron length (note the closeup illustration, not the
generalized skeletal), so using this to argue non-correlation between
Deltadromeus' "pubis" and 1912 VIII 82 is flawed.>

  Though I can see these points are well thought out, I must argue in favor of
Sereno et al. (1996) in regarding the composition of their type. The pubes
comprising part of the type of *Deltadromeus* are extremely large and larger
than expected for the ischia of basal coelurosaurs, even that of an
ornithomimosaur which bear elongated ischia. There is an apron between the
elements, and while I identified a pair of pubes as possible ischia based on
their apparent obturator processes, I must state that the pubes of some
theropods, including tyrannosaurids, ornithomimosaurs, and abelisaurids, are
also extremely narrow for most of their length. Their size also speaks of their
identification as pubes.

  I would also like to note that the pubic material of *Deltadromeus* does, in
fact, include more than the distal end, but also pertains to more of the shafts
than shown, including the apron, leading the Abraczinkas and Sereno to restore
the skeleton with a more complete pubis than the close-up shows on the  distal
pubic morphology.

<So, there is no holotype Deltadromeus pubis to compare to Bahariasaurus'. This
eliminates two characters Sereno et al. used to differentiate the taxa.>

  As noted above, this is not likely. Sereno et al. (1996) included the large
portion of the ischium as part of the type, and this, if including the pubic
length as preserved, from both sides, would involve a rather bizarrely huge
ischium, with a distal ischial profile remarkable identical to that of the pubes
of avetheropods, as in distal view (pers. obs.) the "ischial" boot is triangular
in aspect, narrower caudally than cranially, with an up-turned cranial process
of the boot, and a tapering one of the caudal margin; the angle of shaft to the
boot shows that, if an ischium, the point pointed ventrally with the expanded
ventral surface facing caudally ... or it pointed so that the longer process of
the boot, with the "pug-nosed" tip was caudal rather than cranial, and this
tends to fly in the face of other distal ischia which show an enlargement of the
distal end to correspond with insertion of the m. pubo-ischio-femoralis
externus; in this manner, the morphology of such an identification would not be
logical. In ischia, even when the distal end is expanded in such a manner, the
ischial boot is not expanded laterally.

<Determining the identity of the three non-holotype pubes is difficult.  1912
VIII 81 isn't Bahariasaurus, but 1922 X 48 and 1912 VIII 62 (proximal only) are
only shown in lateral view, so cannot be compared to Bahariasaurus. They compare
well to each other, and are possibly conspecific, though 1922 X 48 in particular
is more robust than 1912 VIII 81 and has a fainter sigmoid curvature that is
positioned differently along the shaft.  This could easily be ontogenetic or
individual variation however.  1922 X 48 and 1912 VIII 62 may be Bahariasaurus
or the same taxon as 1912 VIII 81 (which may be Deltadromeus for all I know).>

  This material, however they may "not be referable" is not very beyond the
point of being moot. I noted above that I made a tentative ID of 1912 VIII 82
(pl.II, fig. 2, pg.42-43) as an ischium because it resembled that of
*Elaphrosaurus.* It also closely resembles the pubes of *Dromeceiomimus*,
including the caudally everted dorsal margin of the pubic apron, which occurs in
several tetanuran theropods. The other pubes are largely irrelevant, as Stromer
identified them as "gen. et sp. indet." with the exception of  1912 VIII 81
(possible juvenile, referred to *Bahariasaurus*), in which the details of the
pubis, excepting proportional differences and position of the pubic fenestra,
and the unfigured but present lack of curvature (Stromer, 1934: pg. 30 "Von dem
Os pubis des Carcharodontosaurus (1922 X 46, Stromer 1931, Taf. I, Fig. 13a-c)
unterscheidet sich das Stück erheblich, denn sein Vorderrand ist gerade und der
Schaft nicht allmählich nach oben zu verbreitert, sondern plötzlich;" which is
translated as "From the OS pubis the Carcharodontosaurus (1922 X 46, Stromer
1931, Taf. I, Fig. 13a-c) the piece differs substantially, because its front
edge is straight and the shaft not gradually widened upwardly, but suddenly.")
That is, the pubis was relatively straight cranially. This agrees well with
*Deltadromeus,* in fact.

  1922 X 48, found near the type of *Bahariasaurus,* is distinct in the slight
curvature of the shape, and the presence of a rather distinct caudal process of
the boot; there is no iliac peduncle, just the facet for the ilium, and in this
it is fairly small. However, only the distal end can be compared to
*Deltadromeus*, and in this it does not appear to be at all consistent. In 1912
VIII 62,

<Sereno et al. referred 1912 VIII 62 to Deltadromeus, presumebly based on
association between it and the coracoid and hindlimb material of 1912 VIII.  But
of the latter material, the pectoral girdle appears to be spinosaurid (see
below), and the femur and tibia are not from the same individual (the tibia's
much smaller) and are not referrable to Deltadromeus either.  Only the fibula
may be, so Sereno et al.'s referral of 1912 VIII 62 to the latter taxon is
unsupported at present.>

  Which was, oddly enough, what I said. Also note that Stromer considered the
femur and tibia to be distinct from one another as far as individuals go; one,
he was neither stupid or silly, and two: he was a very competent anatomist. The
tibia is specimen 1912 VIII 78 (pl.III, pig. 8, pp.40-41), referred to aff.
*Erectopus* (which the femur, 1912 VIII 69, was not -- see previous post on
this), and there is a clear distinction between size. The tibia is comparable in
superficial morphology, and its mention in the previous post was to cover the
possible elements of the paper's description in reference to pertaining to
*Bahariasaurus.*

<Unfortunately, Deltadromeus' (holotype) proximal ischium is too poorly
illustrated to compare to Bahariasaurus', and the latter lacks the distal end to
compare to Deltadromeus' apparent distal ischium ("pubis").>

  Aside from comments about the "pubis," this was _also_ what I said.

<I explained before however, this kind of variation is seen between different
Tyrannosaurus rex specimens, so I don't value its significance.>

  And as I said before, Brochu (2003) warns about identifying variations in
proportions and shapes in *Tyrannosaurus* pelves because you set yourself up
fallen strawmen. There is simply not enough data to know whether ischial
variation reflects individual, sexual, or specific variation. It should also be
noted that the ischium of 1922 X 47 is heavily eroded and partially restored. It
may even therefore preserve a portion of the obturator fenestra, and Stromer
identifies the given margins as broken and the given shape as not representative
of much. The shapes of the pedunculae in *Deltadromeus* are unknown, and the
margins on the cranial margin similarly broken and non-elucidating to their
shape. It is not possible to compare them in any significant way without more
material. What is partially apparent in the type ischium is that the dorsal
margin has a dorsolateral ridge upon it, as in sinraptorine carnosaurs, but this
region is marked by erosion and it, too, is tentative in its comparability.

I wrote:

<<...The lesser trochanter of the two differs in both position and size, ...>>

and Mickey replied:

<I agree completely here, and assume you meant the fourth trochanter differs in
both position and size, not the lesser (=anterior) trochanter.>

  Yes, my boo.

Mickey writes on:

<1912 VIII 69 [referred femur] is not Deltadromeus, though it seems highly
apomorphic with a large tibiofibular crest, distinctly assymetrical distal
condyles, and other characters.>

  The asymmetry of the distal end is apparently an artifact, based on distortion
that also seems to have resulted in the cranial orientation of the femoral head.
Most likely, as in most tetanurans, it was more or less medially oriented;
however, one cannot help but thing that the distortion of the distal end can be
separate from the proximal end, as shaft distortion of bones in the field often
results in just portions of a bone being distorted (the neural spines of _some_
of the dorsals of *Spinsosaurus* are a perfect example, where the neural arch
itself is free of much distortion, and not all spines are as deformed as the two
"wavy" ones).

<Here, I disagree.  The scapula is nearly identical to Baryonyx, differing
mainly in the more flared glenoid margin.  They share the proximodistally deep
glenoid region lacking in Deltadromeus.  The coracoid is also more similar to
Baryonyx, both differing from Deltadromeus by being much shorter
anteroposteriorly, and having a more anteroproximally placed foramen.  They may
belong to Suchomimus or Spinosaurus.>

  I am not sure what is meant by flare of the glenoid margin; I will draw from
both concepts I assume to be likely: ventral deflection from the ventral
scapular surface, and mediolateral flare. The greatest width preserved in the
scapula is given as ~20 cm, and the gross length as preserved is 60+ cm, so that
as preserved the greatest breadth is 1/3 of the preserved scapula, and likely
was only 1/4 when the scapula was complete. This compares well to tyrannosaurs
and *Carnotaurus,* where the glenoid is horrendously broadened to compensate for
holding a small humerus. In *Baryonyx,* the mediolateral flare of the glenoid is
not possible to determine based on Charig and Milner (1997), anyway, as there
are no measurements of the widths of the element to afford comparison. Based on
the other assumption of flare, ventral deflection, it should be noted that in
*Baryonyx*, the glenoid faces partially laterally, whereas in *Carnotaurus* and
*Aucasaurus,* as in 1912 VIII 60, the glenoid faces ventrally, and the margin
between glenoid face and caudal margin of the glenoid buttress is almost a
perfect right angle; in *Baryonyx,* this is a sharply-defined lip, closer to 30
degrees. In *Deltadromeus,* for comparison, the glenoid is partially everted
laterally, but has a shallower angle between glenoid surface and posterior
buttress. The coracoid provides a shallow angle between the scapular and
coracoidal surfaces of the glenoid, whereas in *Baryonyx* they are sharply
inclined. The coracoid is imperfectly preserved, where the cranial margin is
eroded along with the dorsal margin, so it is not possible to determine the
measurements of the coracoid in comparison. Which is why I didn't try. When
articulated, their relative sizes form a complex that is, rather than
incongruent, very similar to *Deltadromeus* and abelisaurids. Because of their
disarticulation and lack of association with other material, it is not possible
to determine their relative size to the skeleton. While I similarly cannot argue
they do _not_ belong to *Spinosaurus,* I am almost certain their morphology does
not permit their referral to a *Baryonyx*-like morphology as forwarded by
Mickey.

<I'd say they are quite possibly synonymous, but this is unverifiable given the
published data.  We've seen there were at least three taxa in the Baharija
Formation, so you can't assume the referred material belongs to Bahariasaurus.>

  I had hoped to, in my own posting, make this quite clear; it may be noted that
I concern myself with synonymy between type specimens, rather than referred
material except where morphologically congruent. Which was why I discussed all
the possible convergent material that could be applied to *Bahariasaurus* versus
any other taxon. That Stromer identified *Spinosaurus,* *Carcharodontosaurus,*
*Bahariasaurus,* material referred to *Erectopus* and *Elaphrosaurus,* and
several unidentified elements, part of which resembles that of the type of
*Bahariasaurus* or appears to represent a similar phylogenetic position as in
"basic tetanuran, abelisaurid" or even spinosaurid. That portions of the type of
*Bahariasaurus* relate to *Deltadromeus* in general terms does not allow us to
provide enough consensus on their synonymy, but certainly does not suggest they
are too different to be related. Previous points on the pubis of *Deltadromeus*
being an ischium are not based on any ischiadic characters, but similarities to
an ischium(?) from the Baharija beds themselves, in which *Deltadromeus* is not
unequivocally present. Otherwise, the material does not so much as attempt to
corroborate *Bahariasaurus* in its distinction (the pubis is sufficient to do
this) but to attempt to see if *Deltadromeus* was in the Baharija, and perhaps
assess its relationship to *Bahariasaurus.*

<This leaves us able to compare only the proximal ischium, which is illustrated
too poorly in Deltadromeus to do such.  Some material from the Baharija may be
referrable to Deltadromeus (notably the fibula 1912 VIII 70), and some to
Bahariasaurus (the proximal ischium 1912 X 47), but neither can be compared to
the other taxon.>

  Except for the pubis. Let's not forget the pubis. ;)  Seriously, the further
comments on the identity of comparability in ischia between the two, depending
on referral of the type pubes in *Deltadromeus* as a second pair of ischia, is
based on deformed result for ischiadic morphology that is merely a pubis in
disguise. Morphology indicates the material is a pubis, despite its superficial
"booted" appearance to ischia of *Elaphrosaurus.*

  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)