ANATOSAURUS

formerly Trachodon, genus of bipedal duck-billed dinosaurs, or hadrosaurs, common as fossils in Late Cretaceous rocks (97.5 to 66.4 million years old) of North America; closely related forms have a worldwide distribution. Anatosaurus, a very large reptile, grew to a length of between 9 and 12 m (30 to 40 feet) and was heavily built. The hindlimbs and pelvic girdle were very well developed. The skull was long and the beak broad and flat, much like a duck's bill. Several hundred rather blunt teeth were present in the jaws at one time; not all were functional simultaneously, but, as teeth were worn or lost, they were replaced by new ones. It is probable that Anatosaurus was aquatic to a certain degree; its tail was compressed laterally, much like the tails of crocodiles. Some Anatosaurus specimens have been found remarkably well preserved as desiccated mummies; in these, skin and internal structures remain. Anatosaurus had webbing between the toes, a further indication of its partially aquatic habit. The outer hide was very leathery and rough. Anatosaurus fed mostly on twigs, seeds, fruits, and pine needles; no remains of aquatic plants have been found in its stomach. It seems likely that the aquatic habit of Anatosaurus was a means of escaping predators and that they fed while on land rather than in the water.