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

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

Jaime Headden wrote-

>   Discussion with Mickey on this taxon prompted a critical review of what
> Stromer (and virtually no other except to repeat him or add little other
data)
> had to say and figure of this form.

A great idea.

>   Comparative data is achievable between the type materials of the two
taxa
> through the distal pubes and proximal ischium. Problematically, Stromer
did not
> illustrate the type pubes in lateral view, merely in caudal view. A
referred
> pubis, that of a "juvenile" 1912 VIII 81, bears comparative boot
morphology,
> though the shaft of the pubes are sigmoid, whereas in *Deltadromeus* they
are
> straight in profile. The distal pubes in *Deltadromeus* are strongly
constricted
> distally, forming a very narrow and shallow pubic apron and bear not
foramen
> between them or between the distal ends of the boot, as in *B. ingens.* In
fact,
> only one pair of pubes from the sites compares to this in general, and
that is
> in fact 1912 VIII 81 in which they are strongly constricted distally,
although
> they bear a large foramen in the above the booth, and the apron is 75% of
the
> pubic length, unlike in *Deltadromeus*. The previously identified
> *Elaphrosaurus* ischia bear similarities to the pubes in lacking any
foramina
> and their strong distal constriction, but the conjoined ischiadic apron is
much
> too extensive to relate.

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.
So, there is no holotype Deltadromeus pubis to compare to Bahariasaurus'.
This eliminates two characters Sereno et al. used to differentiate the taxa.
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).  Sereno et al. referred 1912 VIII 62 to
Deltadromeus, presumedly 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.

>   The proximal ischia are distinctly incomparable, as the proximal ends of
it in
> both taxa are far too incomplete to illustrate details.

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").  Sereno
et al. say the proximal ischia differ in that the ilial peduncle is narrower
in Bahariasaurus.  As I explained before however, this kind of variation is
seen between different Tyrannosaurus rex specimens, so I don't value its
significance.  Besides 1912 VIII 82 and Bahariasaurus' holotype, there are
two other illustrated ischia.  1911 XII 23 and 1912 X 47 (referred to
Deltadromeus by Sereno et al.), both known only from the proximal portion.
Bahariasaurus' differs from 1912 VIII 82 in minor details (slightly shorter
posterior corner of ilial peduncle, more projecting ventral corner of pubic
peduncle[caused by breakage?]) and has a more proximally placed obturator
process.  Although seemingly having a deeper pubic peduncle than either,
1912 X 47 is more similar to Bahariasaurus in having the proximally placed
obturator process and has an even shorter posterior corner to its ilial
peduncle.  1911 XII 23 is too incomplete to comment on, though it is very
similar to the other three ischia.  As stated above, 1912 VIII 82 compares
well to Deltadromeus, but distal ends are missing from the other known
ischia, preventing comparison.

>   The femora compared show similar morphology of the distal end and of the
> anterior trochanter, which is large and aliform or wing-like. The femoral
shaft
> in *Deltadromeus* is illustrated as having a slight curvature, whereas
that of
> 1912 VIII 69 has a far more distinct curvature, though likely this is
based on
> size differences, and is arcuate, whereas *Deltadromeus* has a slightly
sigmoid
> femur in profile. The femoral head in *Deltadromeus* appears to be
oriented
> medially, given the figures in Sereno et al., which is how they coded this
taxon
> (as
> in Coelurosauria); the femur of 1912 VIII 69 has a craniomedially-oriented
head,
> as in ceratosaurs and carnosaurs. The lesser trochanter of the two differs
in
> both position and size, where in the Egyptian femur, it is small and
situated
> below the proximal 1/3 of the femur; in *Deltadromeus*, the lesser
trochanter is
> large and in the proximal 1/3.

I agree completely here, and assume you meant the fourth trochanter differs
in both position and size, not the lesser (=anterior) trochanter.  1912 VIII
69 is not Deltadromeus, though it seems highly apomorphic with a large
tibiofibular crest, distinctly assymetrical distal condyles, and other
characters.  It resembles Baryonyx somewhat.  Notably, both 1922 X 45
(referred to aff. Erectopus) and another smaller distal femur (which I don't
have the number of, table III, 9a and b) lack these characters, and differ
from each other significantly.  Whether either is similar to Deltadromeus is
unknown due to illustration quality in Sereno et al..  At least three taxa
are represented

>   The proximal tibia of  1912 VIII 78 does indeed bear superficial
similarities
> to *Deltadromeus*, however this is only in profile and in general when
seeing it
> from the proximal surface end-on; a channel runs along the Egyptian tibia
front
> to back between the rear condyles and lateral to the cnemial crest, but
not in
> *Deltadromeus*, and the lateral cnemial crest is very sharply angled in
dorsal
> view, as is the lateral femoral condyle, whereas these are far rounder and
> blunter in *Deltadromeus.*

Is this the one in table III 8a/b?  If so, I agree here too- it's not
Deltadromeus.  Both also seem different from Stromer's Elaphrosaurus sp.
(1912 VIII 76, 190), which shares a combination of primitive and derived
traits with "Allosaurus" tendagurensis.  So again, at least three taxa.

>   The fibulae compare very well, and in fact, except for apparent broader
> expansion of the proximal end compared to *Deltadromeus*, and the less
> well-defined margins for the medial fibular fossa, which also expand
closer to
> the edges of the proximal end in 1912 VIII 70, these are identical, and
Sereno
> et al. would not be amiss in referring them to *Deltadromeus.* Since the
type of
> *Bahariasaurus* does not include the fibula, this does not affect their
relative
> synonymy or the nature of the diagnostic status of the latter.

Agreed.

>   The coracoid and scapula (1912 VIII 60) are, for all intends and
purposes,
> identical to *Deltadromeus*, as far as their partial preservation permits
> comparisons, save some small details of profile differences: the coracoid
> possess a more concave margin between the glenoid and tip of the
caudoventral
> process; the scapula proximal end is deeper towards the glenoid than in
> *Deltadromeus.* It is not possible to tell how much larger or smaller the
> complete scapulo-coracoid was to *Deltadromeus.*

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 would also point out other caudal vertebrae that Stromer described
include
> smaller centra with large pleurocoels surrounded by fossae, possibly
distal
> carcharodontosaurid caudals [or something more spectacular, a
therizinosaur?],
> that has implications for the identification of a similar caudal-based
taxon,
> *Inosaurus*, also from Africa ... so, not a therizinosaur, but possibly a
> carcharodontosaur?)

Assuming I've translated the description correctly, Inosaurus is not
reported to have caudal pleurocoels and none are apparent from the figures.
It primarily resembles segnosaurs (specifically Nothronychus) in the large
chevron facets, though comparisons in general morphology can be made to
Yangchuanosaurus and Nomingia as well.

>   So are they the same?
>   No. There is little comparative data between the type and the material
assumed
> to pertain to it, even forbidding Stromer's tentative assignments.
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.
> Features of the referred material (caudal morphology, fibular fossa)
indicate
> the presence of *Deltadromeus* or a very closely related taxon exists at
> Baharija.

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.  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.  The complete ischia 1912 VIII
82 compare well to Deltadromeus distally and differ in small ways from
Bahariasaurus proximally, but I don't think a referral to the former is
warranted given the meager comparison possible, and the fact we don't know
how closely they resembled Bahariasaurus distally.

Mickey Mortimer