 The holotype and paratype ( OMNH 10146 and OMNH <unk> ) , discovered in the early 1940s and described at the same time in 1950 , consist of two partial skeletons and a piece of skull material from the Antlers Formation in Oklahoma . Two much more complete specimens were described in the 1990s . The first ( SMU <unk> ) is a partial skeleton , missing most of the skull , recovered from the Twin Mountains Formation of Texas and currently part of the Fort Worth Museum of Science and History collection . An even more complete skeleton ( NCSM 14345 , nicknamed " Fran " ) was recovered from the Antlers Formation of Oklahoma by <unk> Hall and Sid Love , prepared by the Black Hills Institute in South Dakota , and is now housed at the North Carolina Museum of Natural Sciences in Raleigh . This specimen is the largest and includes the only known complete skull and forelimb . Skeletal elements of OMNH <unk> are almost the same size as comparable bones in NCSM 14345 , indicating an animal of roughly the same size , while the holotype and SMU <unk> are significantly smaller . 
