Casually Walking

Early theropods did not need to be as enormous as Tyrannosaurus for a number of reasons, chief among them being that their prey was not nearly as large as the mega-sauropods and ceratopsians of later ages of dinosaurs. Sinosaurus was still a long predator but possessed a much more gracile body than many following theropods. The dinosaur was definitely still well muscled and had the teeth to terrorize contemporary prey items; however, it is unlikely that it was generating the bite forces of Allosaurus or Tyrannosaurus. Sinosaurus may have rivaled and even outraced the other two dinosaurs, based on the gracile body, but tests of this sort of hypothesis has not been conducted on Sinosaurus so we cannot do more than speculate. The body of Sinosaurus is estimated to have been approximately 5.6 m (18 ft) long, making it shorter than the similar-in-appearance Dilophosaurus which measures 6 m (20 ft) long. Dilophosaurus, which appears in the fossil record a few million years prior to Sinosaurus was probably the largest carnivore in its ecosystem, if not globally, at the time and Sinosaurus may have held a similar distinction. Aside from being the largest animal, a large portion of the length of Sinosaurus (as in Dilophosaurus) was made up of tail.

©Dmitry Bogdanov (as Dilophosaurus sinensis, jr. synonym)

As we know from dromaeosaurs and hadrosaurs a long stiff tail is a great counterbalance for running. However, the tails of Sinosaurus specimens does not appear to be stiffened and instead appears to be appreciably flexible instead. All of the largeness and gracility to this point has pointed to a terrific carnivore outpacing and overshadowing all of its prey items. A flexible tail, though, points less toward high speed running, so it is possible that despite appearing capable of producing significant speed (in relation to other dinosaurs) Sinosaurus may not have needed speed or it may not have required a stiff tail for specific counterbalancing; that is, it may not have accelerated or sustained speeds in the same way that later stiff-tailed dinosaurs did. There also exists the possibility that there was not a great amount of speed at the command of Sinosaurus and its gracile frame and appearance of potential speed is, like its similarity in appearance with Dilophosaurus, merely an impression of a character that we have attributed to it hypothetically, but falsely.