 It is known almost exclusively from a number of "coracoids" (a bone in the shoulder girdle).These have a distinct enough anatomy, however, to allow it to be distinguished from other birds, and even for distinct species to be recognized.The first such coracoid to be found (specimen number YMP 1845, in the collections of the Peabody Museum of Natural History) was first mentioned and informally named by paleontologist Othniel Charles Marsh in the footnote of an 1889 paper, but it was not validly described by him until 1892.