 "Ichthyornis dispar", known from the Niobrara Formation of Kansas, is currently the only valid species of ichthyornithean that is well-supported enough by distinctive fossil evidence to have received a name.However, isolated remains of other ichthyornithean species have been identified.For example, three isolated shoulder bone specimens (RSM P2992.1, UCMP 187207, AMNH 22002) found in the Hell Creek Formation of Montana, Lance Formation of Wyoming, and Frenchman Formation of Saskatchewan have been identified as all belonging to a single species of "Ichthyornis"-like avialan that inhabited this region of North America at the very end of the Maastrichtian age, within 300,000 years of the Cretaceous-Paleogene extinction event 66 million years ago.