FOSSIL FISH FROM THE CRETACEOUS OF THE WESTERN INTERIOR: CLARIFYING THE TAXONOMIC RECORD

Current investigations in the formations on the Missouri River have advanced understanding of Cretaceous fish faunas. Taxa originally described with type specimens from the Eastern Seaboard and Gulf Coasts can now be more readily compared with those described from the Western Interior. Increased knowledge of their anatomy and stratigraphic ranges allows clarification of their classification and nomenclature. The genus Cylindracanthus, as recently reviewed, essentially was advanced from a form taxon to a biological one, based on the dentition, seen for the first time in the first known Western Interior specimen. Possible acipenseriform affinities are hypothesized.

The teleost species Xiphactinus audax, originally described from the Niobrara Group of the Western Interior, is now better known due to additional specimens collected from the Sharon Springs Member of the Pierre Formation (Early Campanian). Specimens from Eastern Seaboard formations of later Campanian age have been previously referred to the species X. vetus. Some of these records are corrected herein.

The enigmatic species Protosphyraena gladius is now known from specimens ranging into the late Campanian and from the Atlantic and Gulf Coasts as well as the Western Interior. While much of the skeletal anatomy is as yet unknown, some taxonomic and nomenclatural details may be clarified by analysis of recently collected specimens.

The new information on the widespread and long-ranging genus Enchodus, of which a thorough review is now in progress, is most valuable for biostratigraphic purposes. By reinvestigation of type specimens as well as the discovery of new material, the taxonomy, stratigraphic ranges, and evolutionary trends of Enchodus species are now better established. Several lineages should prove useful as stratigraphic markers.