Saurophaganax, meaning 'lizard eating master', is a large Allosaurid and a contempory of Allosaurus itself. It was the largest Theropods in its environment measuring 10.9m long and weighing around 3t. One species has been named, S.maximus, however, some paleontologists think it is an Allosaurus and that it should be renamed Allosaurus maximus.
The fossils known of Saurophaganax (both the possible New Mexican material and the Oklahoma material) are known from the latest part of the Morrison formation, suggesting that they were either always uncommon or appeared rather late in the fossil record. Saurophaganax was large for an allosaurid, and bigger than both its contemporaries Torvosaurus tanneri and Allosaurus fragilis. Being much rarer than its contemporaries, making up one percent or less of the Morrison theropod fauna, not much about its behavior is known.