Ischyodus rayhaasi(Chimaeroidei; Callorhynchidae) from the Campanian-Maastrichtian Fox Hills Formation of Northeastern Colorado, USA

Abstract

Modern ratfish (chimaeroids) are examples of a poorly documented lineage of cartilaginous fishes that extends back to Triassic time. Here we report on the discovery of abundant remains of the callorhynchid chimaeroid Ischyodus rayhaasi Hoganson and Erickson 2005 from a Campanian-Maastrichtian age locality in the Fox Hills Formation of northeastern Colorado. A second, distinct group of chimaeroid specimens, designated Ischyodus sp., occurs at the same locality and may represent a species separate from I. rayhaasi, an earlier ontogenetic stage, or sexual dimorphism within I. rayhaasi. The presence of chimaeroid fishes is discussed in regard to the paleoecology and paleogeography of the Late Cretaceous Western Interior Seaway.