An endemic cephalopod assemblage from the lower Campanian (Late Cretaceous) Parras Shale, western Coahuila, Mexico

The cephalopods from Union y Progreso represent the first fossil assemblage described from the Parras Shale in Coahuila, Mexico.Pseudoschloenbachia(Pseudoschloenbachia) aff.P. (P.)mexicana(Renz, 1936),P. (P.)mexicana(Renz, 1936),Baculites haresiReeside, 1927, andMenabites(Delawarella)vanuxemi(Morton, 1830) have a geographically restricted occurrence.Didymocerasjuv. sp.,Menuitesjuv. sp.,Polyptychocerasjuv. sp.,Pseudoxybeloceras(Parasolenoceras)juv. sp., andScaphitessp. ex gr.S. hippocrepis(DeKay, 1828) are represented by juveniles and could not be determined to species level.Desmophyllites diphylloides(Forbes, 1846) is the only long-ranging, cosmopolitan species described from this assemblage. Three new species are described:Eutrephoceras irritilasin. sp.,Hypophylloceras(Neophylloceras)arturoin. sp., andTetragonites silencioensisn. sp. The morphotypeBaculitesn. sp. is also inferred to be distinct. The faunal composition of this assemblage indicates a late early Campanian age. This assemblage shows a high degree of endemism. The causes for this endemism are currently unknown and difficult to assess. Nevertheless, the generic composition of the Union y Progreso ammonite assemblage suggests a short-term early Campanian endemic event.