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.
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.
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.