STL Science Center

STL Science Center

22 June 2013

Speculative Crania

The cranial elements of Deltadromeus are missing entirely. It is certainly not rare for skeletal elements of dinosaurs to be missing and skulls are high on the list of frequently AWOL skeletal elements. An interesting question of taphonomy can be posed when we consider this. What happens to all of those heads that are missing from the fossil record? Are heads washed away easily when the flesh is gone or are they dragged away by scavengers that do not wish to share the brains ("zombie" dinosaur scavengers)? Did heads get buried less frequently than other elements of the body? Whatever the reason, it has led to the recovery of Deltadromeus specimens made up entirely, to this point, of post-cranial material. Thus, all of the representations of the head of Deltadromeus are speculations based on presumably related taxa. Typically this means that the skulls are based on other ceratosaurs. This has led to a variety of ornamentation on the skulls of illustrated and mounted Deltadromeus. Typically a ridge of material has been placed above each orbit, similar to those seen in Ceratosaurus.

©Mineo Shiraishi
The cranial ornaments change over time. They are basically all very similar, but the positions, angles, and overall shape of the crests above the orbits change over time and between illustrators and model makers. This reflects not only personal preferences but changing hypotheses concerning the exact nature and potential construction of the skull of Deltadromeus. It is still not certain that Deltadromeus is a ceratosaur also and the skull may therefore have absolutely no ornamentation at all. It is even conceivable that Deltadromeus, as a very basal ceratosaur may lack crests on the skull entirely for that reason. Regardless, there are certain elements of the body of Deltadromeus that are known fairly well. These include the legs and the majority of the caudal vertebrae. The legs and caudal vertebrae are similar to those found in ceratosaurs, thereby aiding the justification that Deltadromeus is a ceratosaur. Seeing as how that is the best evidence and the best fit for known remains, that is where it is positioned in the dinosaur family tree, for now; the legs and may not be telling all there is to know about this interesting dinosaur.

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