Eaters and eatees

With all the variation in theropods, prey surely varied. The most dynamic and irrefutable evidence about the preferred prey of Velociraptor is the so-called "fighting dinosaurs" specimen: Velociraptor with its hind feet half into the belly of a subadult Protoceratops and its hands grasping, or being held in, the jaws of the soon-to-be victim (Figure 9.22).

A specimen of the Late Jurassic coelurosaur Compsognathus is known that contains most of the skeleton of a fast-running lizard. Not only did Compsognathus swallow nearly whole this delectable meal, but it must have captured its victim through its own speed and maneuverability. Other evidence of theropod stomach contents and diet come from Sinosauropteryx (lizards and mammals), Baryonyx (fish remains), and Daspletosaurus (had-rosaurid bones).

Evenly spaced grooved toothmarks on the bones of the sauropods Apatosaurus and Rapetosaurus have been attributed to the local large theropods: Allosaurus and Majungatholus (from the USA and Madagascar, respectively). Toothmarks attributed to Tyrannosaurus are known from a pelvis of Triceratops, and from a thoroughly crunched tail of the duck-billed dinosaur Edmontosaurus (Box 9.1).

Cannibals. And then it's clear that some dinosaurs didn't shy away from a bit of cannibalism. It has been argued that the Late Triassic ceratosaur Coelophysis, based upon the supposed presence of juveniles within the rib cage, was cannibalistic; however, recent work indicates that the juveniles in the rib cage were actually non-dinosaurian archosaurs. On the other hand, Majungatholus apparently didn't avoid the odd conspecific snack: grooved toothmarks matching the spacing of its own teeth have been found on Majungatholus specimens (Figure 9.23). With only one carnivore known on Madagascar from that time with that tooth spacing, the evidence is circumstantial, but damning. We still don't know if such cannibalism occurred on the run, or whether it was the scavenging of sick or dead individuals.

Beyond these few direct observations of dietary preferences, we are left to speculate on who ate whom. Our best guesses are informed by the known theropods and potential prey in a particular place and time - we might pair Tarbosaurus with Saurolophus, or

Troodon with small ornithopods or juveniles of much larger co-existing dinosaurs (such as hadrosaurids).

The invention of pack-hunting could have allowed relatively small animals to bring down much larger co-existing prey - hence the pairing of Deinonychus (3.5 m) packs with the large (7 m) ornithopod Tenontosaurus, a combination that was first suggested when the shed teeth of Deinonychus were found with Tenontosaurus specimens. Whether true or not, these are often the best available data that can be used to address the question of theropod diets (see also Chapter 13).

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