SYSTEMATICS AND TAXONOMY OF SOFT-SHELLED TURTLES (FAMILY TRIONYCHIDAE) FROM THE JUDITH RIVER GROUP (MID-CAMPANIAN) OF NORTH-AMERICA

Four valid species of trionychine trionychid turtles are recognized from the Upper Cretaceous (mid-Campanian; Judithian) Judith River Group, western North America. Cladistic analysis of extant and Judith River Group trionychines supports referral of three fossil species to Aspideretoides gen. nov. and one fossil species to Apalone, the genus of extant North American trionychines. The taxonomic diversity of Judith River Group trionychids is less than that of younger Maastrichtian and Paleocene assemblages from the Western Interior, largely because of the absence of plastomenine trionychids in the Judith River Group assemblage.