A set of ovibovine horn cores collected from Pleistocene sediments in southeastern Idaho provides additional evidence for sexual dimorphism in the helmeted musk ox, Symbos cavifrons. Specimens previously assigned to Bootherium sargenti are placed in synonomy with Symbos cavifrons as sexual dimorphs (females). Bootherium bombifrons is a valid taxon and is probably not closely related to Symbos.
Nelson, Michael E. and Madsen, James H. Jr.
"Occurrence of the musk ox, Symbos cavifrons, from southeastern Idaho and comments on the genus Bootherium,"
Great Basin Naturalist: Vol. 47
, Article 9.
Available at: http://scholarsarchive.byu.edu/gbn/vol47/iss2/9