Collaborative Research: SG: Early evolution of the modern North American freshwater fish fauna: New Late Cretaceous sturgeons, paddlefishes, bowfins, and teleosts from North Dakota

Field Museum Of Natural History, Chicago IL

Investigators

Abstract

The Late Cretaceous, from 100 million to 65 million years ago, was a time of great change for the freshwater fishes of North America. Many older groups of fishes were going extinct and being replaced by modern groups. But where did the modern groups come from, and how and why did they replace the older groups? These questions, among others, are unanswered because the fossil record of fishes from this time period is extremely poor. This project analyzes newly discovered, complete fossilized skeletons of freshwater fish from a critical time period (72-66 million years ago). These fossils are extraordinarily well-preserved, providing a rare glimpse of complete skeletons. This project will fill a critical gap in understanding the origin and evolution of modern freshwater fish. In addition to the scientific merit of this project, there are several broader impacts. First, the fossils to be described are deposited in publicly accessible natural history collections, thereby ensuring that they are available in perpetuity to the scientific community. Second, student training programs developed around the preparation and analysis of the fossils provides valuable research and training for budding scientists. Third, results from this study will be published in scientific articles and presented at professional meetings and seminars for public audiences. And finally, by using the resources available at the Field Museum of Natural History in Chicago, the project will increase public understanding of science. All specimens will be prepared in a lab where active preparation and study of the specimens can be observed by the more than 1.2 million annual visitors to the Field Museum, including many K-12 student groups and teachers, and a temporary exhibit of this exquisitely preserved fossil fish fauna will add an important component to current exhibits at the Field Museum. Although the modern freshwater fish fauna of North America has been intensively studied, its origin, biogeography, and evolutionary history are still poorly understood, due in part to a lack of whole-body fossils from Cretaceous freshwater deposits, particularly those containing articulated skeletons. This study uses exceptionally well-preserved fossil fish from a recently discovered lagerstatten in the Maastrichtian Hell Creek Formation of North Dakota, to illuminate the transition between the early Mesozoic (consisting of extinct orders and families) and the modern freshwater fauna. Recently discovered blocks containing the articulated, complete skeletons of many freshwater fish have been acquired by the Field Museum for preparation and analysis. All fossils will be described and illustrated using a combination of detailed photographic documentation of all aspects of the anatomy of the species with matched line drawings clearly showing the interpretation of the morphology. These data will form the basis of original morphological descriptions, character conceptualization, and phylogenetic and comparative analyses of key fish lineages present in the blocks, including the Acipenseridae, Polyodontidae, Amiidae, Lepisosteidae, and possibly Teleostei. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.