Details on Capitalsaurus (revised)

["Mickey_Mortimer11" <Mickey_Mortimer11@email.msn.com>]

Tracy Ford wrote-

> Three cheers!  "Capitalsaurus" as been designated as the Official Dinosaur
> of D.C.
>
> To commemorate this special occasion, everyone should go and find the
> crappiest dinosaur fossil they can lay their hands on, and give it a new
> name.  I just can't get enough of those _nomina nuda_ clogging up dinosaur
> taxonomy.

LOL      I nominate Tichosteus aequifacies state fossil of Colorado!
Ah, "Capitalsaurus".....
Over a year ago I wrote a post on this specimen-
http://www.cmnh.org/fun/dinosaur-archive/2000Nov/msg00044.html
At the time, I thought it had a good chance of being diagnosed on
autapomorphic characters.  Since then, I've had the chance to read more
literature and look at some really good photographs of the specimen courtesy
of Tom Lipka.  These have convinced me that the amount of variation within
caudal centra (added to the scarcity of good descriptions) makes
"Capitalsaurus's" unique combination of features inadequate as a dependable
diagnosis.  I was actually given the chance to officially describe
"Capitalsaurus", but my conscience couldn't let me go through with it (of
all the taxa I've written "Details on..." segments of, I'm approached to
describe this one.... sigh  ;-)  ).  Here's a revised Details on
"Capitalsaurus" reflecting my new opinion of it-

* And no, I didn't waste time potentially spent with a new exciting Details
on segment writing this revision.  It was revised for placement on the
Dinosauricon, which must wait until Mike Keesey gets the new version up.  I
know I'm quite behind schedule with the things, and have several taxa I'm
sure would be well liked as subjects (Neimongosaurus, Sapeornis, Kuszholia
(finally got it translated!), but I can either write those, or get done with
my coelurosaur phylogenetic analysis in the near future.  I will get more
written, but when I don't know....

"Capitalsaurus" Kranz 1998
"C." potens (Lull 1911)
= Creosaurus potens Lull 1911
= Dryptosaurus potens Gilmore 1921
Etymology- "powerful capital lizard", as it was found in Washington DC, the
capital of the United States.
Aptian, Early Cretaceous
Arundel Formation, Maryland, USA
Holotype- (USNM 3049) (7-10 m) proximal caudal centrum (140 mm)
Diagnosis- proximal caudal centra slightly opisthocoelous; proximal caudal
centra with single ventral keel.
Description-
The holotype was collected by J. K. Murphy in a Washington D.C. sewer.
Comparison with Allosaurus (Madsen, 1976) indicates that the holotype is
probably from the fifth or sixth caudal vertebra. Based on this, it is
probably from an animal 7-10 meters long.  Although Gilmore (1920) referred
the mid-portion of a large pedal ungual I (USNM 8505) to this taxon, this
was only based on size and provenence.  No valid criterion suggest such an
assignment was warrented, so it will not be discussed further.
The specimen is a proximal caudal centrum missing the neural arch and spine.
In addition, some of the posterior surface has been abraded.  The centrum is
slightly opisthocoelous, with the anterior articular surface slanted
slightly posteroventrally.  It is strongly compressed laterally  (anterior
face 130 percent as tall as wide) and roughly oval in anterior view, with
flattened sides.  The neural canal is broad, though constricted in the
middle.  Ventrally, the centrum shows a single median keel, with a chevron
facet posteriorly. Additionally, the ventral edge is only very slightly
concave in lateral view.  It is cancellous internally and lacks pleurocoels.
Relationships-
Comparison to other theropods is difficult due to both the fragmentary
nature of the specimen and the few detailed descriptions of caudal centra in
the literature.  As "Capitalsaurus" was discovered in Cretaceous deposits,
it is assumed that the centrum did not derive from a basal theropod such as
a coelophysoid or Dilophosaurus, which are only known from the Triassic and
Early Jurassic.  This species has been referred to Allosaurus and
Dryptosaurus in the past, but is stratigraphically closest to
Acrocanthosaurus. It will be compared to these three genera first, then to
other genera that may be similar.
The proximal caudals of Allosaurus are amphiplatyan to slightly procoelous,
the opposite of "Capitalsaurus". Also, they are about as wide as tall,
sometimes wider, and the ventral edge is much more concave. The ventral
surface has a slight groove instead of a keel.
Those of Dryptosaurus share the straighter ventral edge and are slightly
taller than wide (~1.05 times), but no further details can be discerned.
Acrocanthosaurus has caudal pleurocoels (like Carcharodontosaurus, but not
Giganotosaurus), a concave ventral margin and amphiplatyan or amphicoelous
centra. The ventral surface is grooved and the centra are 1-1.2 times taller
than wide.
The only theropod described as having opisthocoelous caudals is the
segnosaur Nothronychus.  This taxon differs from "Capitalsaurus" in having a
median ventral groove, pleurocoels, an autapmorphic posterolateral tubercle,
larger chevron facets and being slightly wider (1.16 times taller than
wide).  Among other segnosaurs, at least Neimongosaurus and Segnosaurus lack
opisthocoelous centra.
Several theropods are known to lack ventral grooves on the proximal caudals.
These include Elaphrosaurus, Carnotaurus, Eustreptospondylus, Suchomimus,
Sinraptor dongi, "Chilantaisaurus" maortuensis, Ornithomimus? sedens and
alvarezsaurids.  Of these, only alvarezsaurids are known have ventral keels,
though the condition in most others is uncertain in this regard.  Although
most other theropods (eg. Ceratosaurus, Torvosaurus, Monolophosaurus,
Nedcolbertia, Sinraptor hepingensis, Tyrannosaurus, Archaeornithomimus,
Gallimimus, Microvenator, Chirostenotes) are described as having a ventral
groove, the condition in Sinraptor dongi at least changes from convex in the
proximal caudals to grooved in the mid and posterior caudals.  This suggests
our knowledge of which theropods have convex ventral surfaces on their
proximal caudals is extremely limited, and subject to change as specimens
are described more fully.  Although alvarezsaurids do have ventral keels,
they are otherwise quite dissimilar to "Capitalsaurus" in having strongly
procoelous centra.  Several theropods are similar to "Capitalsaurus" in
having centra over 1.2 times taller than they are wide, including
Monolophosaurus, sinraptorids and Bagaraatan.  Theropods known to have more
circular centra are Ceratosaurus, Carnotaurus, Elaphrosaurus, Torvosaurus,
Baryonyx, Piatnitzkyosaurus, Allosaurus, Acrocanthosaurus,
Carcharodontosaurus, Dryptosaurus, ornithomimids and oviraptorosaurs (which
are diagnosed in part by their wide caudal centra).  Paravians (barring
alvarezsaurids) have distinctively subrectangular centra, so "Capitalsaurus"
can be excluded from this clade.  The condition found in "Capitalsaurus",
where the ventral edge of the centrum is nearly straight, is extremely rare
in theropods, being otherwise noted in Dryptosaurus, tyrannosaurids and
Bagaraatan.  This can vary greatly with position in some taxa such as
Bagaraatan, so undue emphasis shouldn't be placed on the character.  While
clearly not a derived oviraptorosaur or paravian, the current phylogenetic
utility of proximal caudal centra does not allow placement more precise than
assumed Neotheropoda incertae sedis.  While currently unique compared to
described theropod caudals, the amount of variation between caudal centra in
single specimens is just starting to be revealed (Sinraptor dongi's ventral
groove/keel; titanosaurid's articular surfaces varying from opisthocoelous
to procoelous; Bagaraatan's ventral edge concavity).  Because of this
potentially high variation, I am extremely cautious as to the taxonomic
utility of this caudal centrum and only doubtfully retain it as a valid
taxon.
Reference- Kranz, P. M., 1998. Mostly Dinosaurs: A Review of the Vertebrates
of the Potomac Group (Aptian Arundel Formation), USA, in Lucas, Kirkland and
Estep, eds., 1998: 235-238.

Mickey Mortimer