Tenontosaurus was a large and particularly long-tailed. Its long forelimbs and short, broad hands suggest that is walked on all fours, though it was probably able to rear on its back legs when feeding or fighting. Its skull was deep, and its nostril opening were long. Two species are known. In one, the front of the upper jaw was toothless, but in the other, teeth were present in the same region. The outer rim of the beak at the tip of the lower jaw was serrated.