Nondinosaurian Predators On Dinosaurs

Dinosaurs originated in the Late Triassic (Heckert and Lucas, 1998; Hunt et al., 1998), and started out as modest-sized animals compared with many of their non-dinosaurian neighbors; it is very likely that Triassic dinosaurs frequently fell prey to (or were scavenged by) large phytosaurs and

FIGURE 2—Portion of the fibula of an herbivorous dinosaur (Museum of the Rockies 549, Hypacrosaurus), with a theropod tooth embedded in it (arrow). The exposed portion of the tooth is about 5 mm long.

other predatory non-dinosaurian archosaurs (Hungerbuhler, 2000). Throughout the later Mesozoic, small-bodied dinosaurs (adults or juveniles) were likely eaten by crocodylimorphs (including terrestrial cursorial forms; Kirkland, 1994) and other large reptiles.

The Cretaceous saw the evolution of crocodyliforms that were probably large and massive enough to take even big adult dinosaurs. Sarcosuchus from the Early Cretaceous of Africa is estimated to have reached a total length of 11-12 meters and a body mass of 8000 kg, as large as any known carnivorous dinosaur (Sereno et al., 2001). Deinosuchus, an alligatorid crocodylian from the Late Cretaceous of the southern and western U.S., may have been equally big, and bite marks likely made by this reptile occur in both hadrosaurid and tyrannosaurid bones (Schwimmer, 2002). In the Late Cretaceous of the southeastern U.S., Deinosuchus may have displaced large theropods as the dominant big predator (Schwimmer, 2002), at least near larger bodies of water.

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