A new macrovertebrate assemblage from the late Cretaceous (Campanian) of Southern Utah

[Extract] For most of the late Cretaceous, a shallow epeiric sea subdivided North America into eastern and western landmasses - Appalachia and Laramiclia, respectively. Whereas little is known of Appalachian faunas, Laramidia has yielded an abundant terrestrial fossil record, arguably the best continent-scale example for any Mesozoic time interval. To date, however, the bulk of these fossils have been recovered from the northern portion of Laramidia, in particular Alberta and Montana. The relatively poor fossil record from southern Laramidia has limited our ability to test several key biogeographic and evolutionary hypotheses. In 2000, the Utah Museum of Natural History (now the Natural History Museum of Utah), University of Utah, launched an interdisciplinary project in Grand Staircase-Escalante National Monument aimed at exploring Late Cretaceous terrestrial and freshwater ecosystems preserved within the Kaiparowits Basin. Although emphasis has been placed on collection and study of macrovertebrates, from the outset the "Kaiparowits Basin Project" has targeted a spectrum of data sources, spanning sedimentology, stratigraphy, paleobotany, and ichnology, as well as vertebrate and invertebrate paleontology. This large-scale, interdisciplinary effort has thus far concentrated on two Campanian-aged geologic formations, the Kaiparowits and Wahweap, with spectacular results that include a previously unknown assemblage of dinosaurs and other macrovertebrates. Turtles, crocodylians, and dinosaurs all exhibit relatively high species diversity, with many endemic taxa. The fossiliferous Kaiparowits Formation alone has yielded remains of 14 turtle taxa, six crocodylian taxa, and l6 dinosaur taxa, with evidence that these communities inhabited a wet, largely swampy environment with vegetation ranging from cypress trees (lowest elevation) to dicot forests (better-drained settings) to forests of taxodiaceolls and other gymnosperms (well-drained settings). These and other finds are stratigraphically constrained by multiple radiometric dates, allowing robust comparisons with coeval northern vertebrate assemblages. Considered in unison, five distinct lines of evidence- taxonomy, phylogeny, stratigraphy, paleoenvironment, and biogeography - provide strong support for the vertebrate provincialism hypothesis, which postulates the occurrence of latitudinally arrayed biotic "provinces" on Laramidia for at least a portion of the Late Cretaceous. Paleontologically, the Kaiparowits Formation has now been established as the best-known Campanian unit from southern Laramidia, exceeded in the north only by the Dinosaur Park Formation of Alberta.

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