Specimens similar to "Postosuchus" were discovered in Crosby County, Texas in 1920, and described by paleontologist Ermine Cowles Case in 1922. The fossils were composed only of an isolated braincase (UM 7473) and fragments of pelvic bones (UM 7244). Case then mistakenly assigned these specimens to the dinosaur genus "Coelophysis". In the case of the braincase later assigned to "Postosuchus", in 2002 paleontologist David J. Gower argued that the specimen is not complete and may belong to an ornithodire. Between 1932 and 1934, Case discovered other fossils of caudal vertebrae (UMMP 13670) in Rotten Hill, Texas, and a complete pelvis (UCMP V72183/113314) near Kalgary, Texas. Within the same period, paleontologist Charles Lewis Camp collected over a hundred "rauisuchian" bones, from what is now the Petrified Forest National Park of Arizona, which belong to at least seven individuals (UCMP A296, MNA 207C). Later, more remains came to light. In 1943, Case again described a pelvis along with a pubis (UM 23127) from the Dockum Group of Texas, which dates from the Carnian through the early Norian stages of Late Triassic period. These early findings, from 1932 to 1943, were initially referred to as a new phytosaur reptile, but assigned forty years later to "Postosuchus".