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Here's a little something I've managed to get
together this weekend. It clarifies the status of a taxon many of you have
probably never heard of. Although the name has only been published in a
faunal list as of date, "Capitalsaurus" is indeed based on the holotype of
Creosaurus potens (Lipka, pers. comm. with Kranz 2000). Does this make
"Capitalsaurus" a valid replacement name instead of a nomen nudum, or does the
synonymy have to be published to make it valid? In any case, because the
taxon has been previously described (albeit under a different name), I hope this
doesn't count as scooping Kranz. Instead I hope it publicizes knowledge of
just what the taxon he published was intended to do- provide a stable generic
name for a potentially valid Arundel theropod.
"Capitalsaurus" Kranz 1998
"C." potens (Lull 1911)
= Creosaurus potens Lull 1911
= Dryptosaurus potens Gilmore 1921
Aptian, Early Cretaceous
Arundel Formation, Maryland, USA
holotype- (USNM 3049) (7-10 m) proximal caudal
centrum (140 mm)
Diagnosis- proximal caudal centra slightly
opisthocoelous and show the combination of a single ventral keel and almost
straight ventral edge.
Description-
This species is only known from a proximal caudal
centrum, but comparisons to other large theropods suggest it was seven to ten
meters long.
The centrum is slightly opisthocoelous (perhaps
platycoelous would be a better description), lacks pleurocoels and is much
taller than wide (1.3 times taller than wide). The ventral edge is
almost straight and has a single ventral keel.
Relationships-
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. Comparisons to most genera are difficult
due to poor descriptions.
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.
Ceratosaurus has procoelous centra with deeply
concave ventral margins and a deep ventral groove.
The centra of Carnotaurus are slightly wider than
tall, amphicoelous and have deeply concave ventral margins.
Torvosaurus also has amphicoelous centra with
deeply concave ventral margins. In addition, its ventral surface is
grooved and the centra are subcircular.
A few proximal caudal centra are known from
Baryonyx. These are amphicoelous, taller than wide (1.1 times) and
deeply concave ventrally.
Monolophosaurus has centra taller than wide with
deeply concave ventral margins. The ventral surface has a shallow
groove.
Sinraptor has a centra taller than wide (1.3 times)
and a single ventral keel like "Capitalsaurus",
but its centra have deeply concave ventral margins.
Nedcolbertia has amphicoelous centra with deeply
concave ventral margins. They are slightly taller than wide and have
ventral grooves.
Gorgosaurus has amphicoelous or amphiplatyan centra
with slightly concave ventral margins.
Ornithomimids have centra with deeply concave
ventral margins and shallow ventral grooves that are slightly wider than
tall. Those of Gallimimus are slightly procoelous while Archaeornithomimus
has amphicoelous centra.
Microvenator and Chirostenotes
have centra that are much wider than tall with ventral sulci. Those
of Chirostenotes are amphicoelous and those of Microvenator are
platycoelous. Both Chirostenotes and oviraptorids have
pleurocoels.
Unfortunately, segnosaurs have poorly described
caudal vertebrae, although those of Segnosaurus are said to be
platycoelous.
Bagaraatan has slightly procoelous centra much
taller than wide (1.3 times), some of which have almost straight ventral
margins.
Eumaniraptorans have proximal caudal centra
distinctively rectangular in section, except alvarezsaurids which have strongly
procoelous centra.
Thus, no theropods have a strong resemblance to
"Capitalsaurus" and it is probably not a carcharodontosaurine, caenagnathoid or
eumaniraptoran. The single ventral keel is only known in
Sinraptor. It is unknown whether other sinraptorids exhibit this
condition. Dryptosaurus, tyrannosaurids and Bagaraatan have nearly
straight ventral margins. Several taxa (Monolophosaurus, sinraptorids,
carcharodontosaurids, Bagaraatan) have centra about 1.3 times taller than wide,
like "Capitalsaurus". I know of no theropods with opisthocoelous caudal
centra, but Segnosaurus and Microvenator have platycoelous centra.
"Capitalsaurus" seems to be unique, and thus a valid genus, but it's
relationships remain obscure. I recommend it remain Neotheropoda incertae
sedis.
This example shows that even an isolated bone can
be differentiated from other taxa, although future comparison is needed to
securely validate this genus. Hopefully Kranz will properly describe it
soon. If anyone wants a figure of the centrum, I can send it.
Mickey Mortimer
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