Kenshu Shimada, Cynthia K. Rigsby, Sun H. Kim. Partial skull of Late Cretaceous durophagous shark, Ptychodus occidentalis (Elasmobranchii: Ptychodontidae), from Nebraska, U.S.A.. „Journal of Vertebrate Paleontology”. 29 (2), s. 336–349, 2009. DOI: 10.1671/039.029.0226. (ang.).
Kenshu Shimada, Michael J. Everhart, Ramo Decker, Pamela D. Decker. A new skeletal remain of the durophagous shark, Ptychodus mortoni, from the Upper Cretaceous of North America: an indication of gigantic body size. „Cretaceous Research”. 31 (2), s. 249–254, 2010. DOI: 10.1016/j.cretres.2009.11.005. (ang.).
