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



Jaime Headden wrote-

> 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.

The idea of Deltadromeus' "pubis" being an ischium wasn't originally mine,
it was Longrich's (see http://www.cmnh.org/dinoarch/2000Nov/msg00067.html ).
Specifically, when I asked him for his reasoning, he replied with the
following (I had lost this e-mail for a while, which is why I haven't
credited Longrich yet [wasn't quite sure it was him] or brought up his
points).

"For
one thing, pubes virtually always have a fenestra located between the boot
and apron- whether it's Carnotaurus, Allosaurus, Unenlagia, whatever. This
is not present in the "pubes" of Deltadromeus.
Second, if you put two cylinders together you get a sort of
double-cylinder " OO " cross-section to them (which is how pubes are in
their distal segment)- so you get an anterior groove that runs down the
front between the shafts of the pubes, and then it opens up into an
anterior cupping or "scoop" formed in between the two boots. You could
probably rest a ball in this place in Tyrannosaurus or Allosaurus or
whatever. However, Deltadromeus doesn't have this- anteriorly, from the
"anterior edge of the pubic boot" running dorsally is a single sharp
midline ridge, not a cupped area and groove. This is nothing like the vast
majority of theropod pubes, but it is rather like the posterior edge of
many ischia, in particular if you look at the ischial boot of Elaphrosaurus
you will see the exact same thing, including the ridge and the strongly
triangular shape of the boot. The Elaphrosaurus ischial boot is incredibly
similar to the Deltadromeus ischial boot, in fact.
Third, the shafts of the booted element are tightly appressed for
what must have been at least a third or a half of their length- there is no
room for a pubic apron. Instead of a midshaft cross-section like O--O, you
have a cross section sort of like () for most of the length of the shaft.
This doesn't look like pubes, but it does look like ischia which have flat
medial surfaces where they contact each other, and rounded lateral
surfaces, so if you start to join them together you're going to get sort of
a single columnar shaft. Which is what the Deltadromeus "pubis" looks like.
Fourth, the boot is completely coossified front and back. Although
pubes are usually tightly coossified posteriorly, they usually do not
coossify anteriorly (there are a few exceptions, but they are maniraptorans
such as Caenagnathus or Avimimus).
Finally, I started digging around in the cabinets and found all
kinds of remains that, when compared to an allosaur pubis, started making
one heck of a lot of sense. So the "pubis" looks completely wrong for a
pubis, looks completely correct for an ischial boot, and there are scraps
that really look like they belong to the shafts of a regular pubis."

So basically, there is no interpubic foramen, no anterior longitudinal
midline groove, no pubic apron (contra you), it fuses completely anteriorly,
and there are different pubic remains preserved.  Sounds quite reasonable to
me, and from someone who's actually examined it first hand.  More than can
be said for you or I.  Your information regarding the unpublished morphology
comes from unclear photos of the mounted skeleton, in which I can not see an
apron between the bones.  Furthermore, the extent of real bone is
indeterminable from the photo. The ischia may be large for a coelurosaur,
but not for a ceratosaur.  Even tyrannosaurids (Maleev, 1974) and
ornithomimids (Osmolska et al., 1972) have broader pubes than would be true
in Deltadromeus, and that of abelisaurids (Kellner and Campos, 2002) is
broader yet.  If Longrich is right about pubic scraps being present, they
might shed light on the synonymy issue.

> 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.

Perhaps, but exactly how much?  The skeletal also differs from the closeups
in how much of other elements are known (eg. scapulacoracoid, humerus).  I
don't believe it's very trustworthy in this regard.

> <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.

As above, trusting Sereno et al.'s skeletal reconstruction to be accurate in
respect to the exact amount of bone preserved seems unwarranted.  Though I
don't feel the photo of Deltadromeus' skeleton unambiguously shows the
"pubic" foot to be triangular in distal profile, the ischial foot of
Elaphrosaurus is anyway (Janensch, 1925), narrower anteriorly than
posteriorly (which would be reversed if it were a pubis of course),
resembling what you describe for Deltadromeus.  The angle between the foot
and shaft in Deltadromeus (~50 degrees) is intermediate between Carnotaurus
(~60; Bonaparte et al., 1990) and Elaphrosaurus (~40), so presents no
problems.  Obviously the longer process was posteriorly pointed, it would be
ridiculous and nearly impossible to articulate otherwise.  This resembles
Elaphrosaurus to a large degree, which even shows an (albeit lesser
developed) upturned posteroventral surface and exhibits lateral expansion.
Note 1912 VIII 82 has an even more developed upturned posteroventral
surface.

> 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.

I still say 1912 VIII 82 is an ischium, regardless of the presence of a
posteroventrally everted pubic apron in some taxa.  The distal narrowness,
absence of an interpubic foramen, the wider and shorter separation
proximally between the shafts, and the narrow (in lateral view) ilial
peduncle all argue for this.
Deltadromeus' "pubis" is narrower than 1912 VIII 81, lacks an interpubic
foramen, has a narrower anterior foot, and an anterior midline longitudinal
groove.

> 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,

I take it you're basing the straight shaft, absent posterior foot and large
ilial peduncle of Bahariasaurus on the translated text?

> <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.

All the more reason not to support separation of taxa on that character.

> <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.

By "flared glenoid margin"I meant the ventral deflection from the ventral
scapular surface.  As both Baryonyx and Deltadromeus have a laterally angled
glenoid, I don't think its absence in 1912 VIII 60 has much relevence to our
debate.  It angles laterally in Carnotaurus too, while Aucasaurus' is
undescribed.  The 45 degree angle between glenoid surfaces in 1912 VIII 60
is smaller than the 90 degree angle in Baryonyx, true.  This is an
additional difference between the specimens.  1912 VIII 60 further differs
from Deltadromeus is having a larger glenoid compared to coracoid height
(35% of total proximodistal height, vs. 20%; 34% in Baryonyx).  Though
clearly broken in some areas, other edges (anteroproximal corner,
posterodistal edge, posterior edge) look natural.  I don't see much
resemblence to Carnotaurus, perhaps you would point it out?

> <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.

It was less than clear to me-
"However, if
one assumes that the type and referred material DO pertain to a single
taxon,
this form does possess some distinct features from that of *Deltadromeus*,
including the distal pubic morphology, that shows they are separate taxa."
"Tetanuran features of *Bahariasaurus* include:
  305.1, pubic peduncle of ilium longer craniocaudally than it is wide
(based on
the proximal pubis);
  341.1, distal femoral extensor groove shallow and just barely conspicuous;
  352.1, tibia backs distal end of fibula and calcaneum;
  362.1, astragalar ascending process mediolaterally reduced.
ACCTRAN optimization provided: 334.1, anterior trochanter divided from
greater
by deep cleft;
  360.1, fibula distal end less than twice the width of the mid-shaft, with
reduced dorsal fossa on astragalus/calcaneum/tibia for articulation of the
distal end;
  364.1, astragalar distal ends oriented craniocaudally.
DELTRAN optimization provided: 338.2, no trochanteric shelf."
"So they would appear to be, by some extent, relatively close, basal
tetanurans, perhaps abelisaurs convergent upon tetanurans, or a moderate
taxon;"
If you don't concern yourself with referred material, why almost exclusively
use referred material to place Bahariasaurus phylogenetically?

Mickey Mortimer