I love B-grade monster movies, and one of my all time favorites is the 1980 creature feature Alligator. As its title suggests, the film's protagonist is a 40-foot-long alligator, literally pumped up on steroids from consuming the bodies of medical research lab animals which had been dumped in the sewers under Chicago, and it spends much of its screen-time chewing the scenery (and cast). What has always made the story particularly appealing to me, though, is that there once were alligators of such prodigious size in North America. Around 80 million years ago, in what is now the western United States and Mexico, the 40-foot alligator
As reported by paleontologists Héctor Rivera-Sylva, Eberhard Frey and José Rubén Guzman-Gutierrez, during the Late Cretaceous the Mexican state of Coahuila was covered by a large delta, and this was the watery home of Deinosuchus. A few vertebrae and osteoderms (the bony components of the armor of crocodylians) of the giant relative of living alligators have been found there before, as well as the remains of dinosaurs, and a hadrosaur vertebra discovered in 2007 shows that Deinosuchus did sometimes have dinosaur for dinner. The dinosaur tail bone contains a toothmark consistent with the damage that the conical teeth of Deinosuchus would have done, and the fact that the remains of the giant alligator were found nearby confirms that it did live in the area in which the dinosaur bone was found.
The question is whether the tooth-marked bone represents an attack on a hadrosaur by Deinosuchus or whether it indicates scavenging by the large predator. Unfortunately, there is no way to know for sure. If Deinosuchus was like its living relatives it would not have turned up a free meal, but the fact that the bitemark is on a tail vertebrae leads the authors of the paper to suggest that the dinosaur was fleeing from Deinosuchus when it was attacked. In this case, the authors speculate, the damage to the dinosaur's body would have been so great that it probably would have died of blood loss or infection soon after the attack. This scenario is certainly possible, but the alternative scavenging scenario cannot be ruled out.
Héctor E. RIVERA-SYLVA, Eberhard FREY, José Rubén GUZMÁN-GUTIÉRREZ (2009). Evidence of predation on the vertebra of a hadrosaurid dinosaur from the Upper Cretaceous (Campanian) of Coahuila, Mexico Notebooks on Geology, 1-6