fracture. This claim was repeated in 1892 by Cope, while arguing that C. nasicornis should be classified as a species of Megalosaurus due to insufficient anatomical differences between these genera. However, examples of fused metatarsals in dinosaurs that are not of pathological origin have been described since, including taxa more basal than Ceratosaurus. Osborn, in 1920, explained that no abnormal bone growth is evident, and that the fusion is unusual, but likely not pathological. Ronald Ratkevich, in 1976, argued that this fusion had limited the running ability of the animal, but this claim was rejected by Paul in 1988, who noted that the same feature occurs in many fast-moving animals of today, including ground birds and ungulates. A 1999 analysis by Darren Tanke and Bruce Rothschild suggested that the fusion was indeed pathological, confirming the earlier claim of Baur. Other reports of pathologies include a stress fracture in a foot bone assigned to the genus, as well as a broken tooth of an unidentified species of Ceratosaurus that shows signs of further wear received after the break. Paleoenvironment and paleobiogeography All North American Ceratosaurus finds come from the Morrison Formation, a sequence of shallow marine and alluvial sedimentary rocks in the western United States, and the most fertile source for dinosaur bones of the continent. According to radiometric dating, the age of the formation ranges between 156.3 million years old (Mya) at its base, and 146.8 million years old at the top, which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. Ceratosaurus is known from Kimmeridgian and Tithonian strata of the formation. The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains. This formation is similar in age to the Lourinhã Formation in Portugal and the Tendaguru Formation in Tanzania. The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs. Other dinosaurs known from the Morrison include the theropods Koparion, Stokesosaurus, Ornitholestes, Allosaurus, and Torvosaurus; the sauropods Apatosaurus, Brachiosaurus, Camarasaurus, and Diplodocus; and the ornithischians Camptosaurus, Dryosaurus, Othnielia, Gargoyleosaurus, and