Down in the bed of the Paluxy River, near Glen Rose in Texas in the United Sates, two sets of footprints show that Acrocanthosaurus was racking it's next meal. It's prey, according to the second set of prints, preserved in the fine sediments of the Glen Rose Formation, was a Pluerocoelus, a giant Sauropod. The prints reveal something of the hunting habits of the giant meat eater. They also show that the Sauropods had developed a defence strategy, with the largest animals on the outside of the herd - like a herd of Buffalo in which th big bulls protect the cows and young from Lions. Durng Early to Mid Cretaceous times, in what is now the south western part of the United States, Acrocanthosaurus was close to being a top predator. It had huge teeth with long roots. The teeth were slightly curved but thin and, unlike those of Tyrannosaurus, probably broke quite easily. The broken tooth was then shed and another one grew in it's place. The meat eater had powerful arms with sharp claws. It was a perfectly balanced hunter, with a strong, muscular back, and it ran on it's hind legs. The 60 cm high (2 ft) spines over the bones of the back would have supported huge muscles.