LATE CRETACEOUS FRESHWATER FISH FROM SOUTHERN UTAH WITH EMPHASIS ON FOSSILS FROM GRAND STAIRCASE- ESCALANTE NATIONAL MONUMENT (GSENM)

Cretaceous strata across southern Utah preserve a relatively continuous record of terrestrial vertebrate life, as well as that of the associated freshwater fishes. Much of this freshwater fish record is derived from wet screen-washing of microvertebrate localities within the GSENM. Fossils recovered in Utah represent each stage of the Cretaceous from the latest Albian (100 mya) to the late Maastrichtian (65 mya), with those from GSENM ranging from about 95-70 mya. Although consisting only of isolated teeth and bones, significant patterns and events in the development of North America’s freshwater fish fauna may be recognized. Fossils from the Cedar Mountain and Dakota formations (approximately 100 mya until 93 mya) document that, until the end of the Cenomanian, freshwater fish faunas had a decidedly primitive aspect to them and consisted principally of three types of elasmobranchs, lungfish, diverse holostean-grade osteichthyans, and primitive teleosts. At the end of the Cenomanian, a significant extinction occurred among marine taxa. This extinction is largely unreflected in terrestrial faunas. However, there is a distinct faunal turnover documented among freshwater fishes in southern Utah. Much of the diversity of the holostean-grade osteichthyan fish is lost, particularly the previously abundant and diverse semionotid fishes. In addition, lungfish nearly disappear completely in western North America. Turonian freshwater fish faunas documented in the 91.5 my old Smoky Hollow Member of the Straight Cliffs Formation are considerably less diverse, consisting mostly of amiids, gars, rays, and a few teleosts. Over the remainder of the Late Cretaceous, as documented by the Coniacian-Santonian John Henry Member of the Straight Cliffs Formation, and the lower Campanian Wahweap and upper Campanian Kaiparowits formations, freshwater fishes diversified. At least five lineages of freshwater elasmobranchs are well documented in these strata, and these are unique in all becoming extinct at the end of the Cretaceous, whereas the rest of North America’s fish fauna continued to diversify into the Cenozoic.