In 1869, Dr. Ferdinand Vandeveer Hayden obtained a second hand
fossil of an Allosaurus vertabrae that had come from Colorado. He
sent it to Joseph Leidy, who in turn assigned it to the new genus
Antrodemus. It is now known that this was an Allosaurus fossil. In
1877, Othniel Charles Marsh found some fragmentary remains of
Allosaurus, which he then named Allosaurus fragilis.