STL Science Center

STL Science Center

08 April 2016

Heads and Tails

To start discussing the body in more skeletal detail, the tails of Dilophosaurus are well known. The holotype animal is actually quite nearly complete. This is somewhat rare for large fossil animals, though Dilophosaurus is still somewhat small by dinosaur standards. This is what allows for the inferred skeletal elements of Sinosaurus however and we do benefit from the completeness of one dinosaur in comparison with a second dinosaur. Sinosaurus, though, has a well preserved skull in a few specimens and a juvenile specimen is included in that number. The juvenile skull, and a number of the adult skulls, are disarticulated. Disarticulation can be a very beneficial outcome of fossilization; a well articulated fossil skull is good for showing a complete entity whereas the disarticulated skull can be used to show how bones of the skull are sutured and put together into the solid structure.

Sinosaurus cranial elements are well known because of all of these specimens. This allows us to identify individual bony elements and differentiate them from other animals (aiding in justification of separating the genera/species). The teeth of Sinosaurus are also helpful in this matter. These teeth are serrated on both the anterior and posterior edges and flattened width-wise. This means that Sinosaurus' teeth are actually somewhat shark-like in their construction and would cut flesh on biting down and pulling back and away with the teeth. Those inferred actions are more closely related to animals like the dromaeosaurs with recurved posterior serrated teeth. Sinosaurus had recurved teeth as well, making the comparison worthwhile, but the anterior serrations are much more useful for cutting into flesh during the powered closing of the jaw. The anatomy appears to indicate the idea that Sinosaurus was biting and cutting its prey at the same time and then pulling and making a second cut as its teeth were moved away from the prey. That sort of wound would be hard for any animal to recover from and might explain some hunting hypotheses related to these animals.

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