Baenid turtles of the Kaiparowits Formation (Upper Cretaceous: Campanian) of southern Utah, USA

摘要

I describe the assemblage of baenid turtles found in the Campanian Kaiparowits Formation of southern Utah and compare it with baenids from other basins across Laramidia. Baenids were one of the most diverse and abundant freshwater turtle clades during the Late Cretaceous. They were restricted to North America, with all except the basal-most taxon (Arundelemys) restricted to Laramidia. During the Campanian, baenids were conspicuous parts of the turtle assemblages of Alberta, Montana and New Mexico. The baenids of the Kaiparowits Formation are critical in that they provide an assemblage from southern Laramidia that is correlative with those from northern Laramidia, allowing for more accurate testing of Campanian palaeobiogeographical hypotheses. In this paper, two new baenid species, Neurankylus hutchisoni sp. nov. and Neurankylus utahensis sp. nov., are described. Additionally, the first description of cranial material from Denazinemys nodosa is provided. A comprehensive survey of collected material indicates mat at least six baenid taxa are present in the formation, including Neurankylus hutchisoni, Neurankylus utahensis, Thescelus sp., Arvinachelys goldeni, Denazinemys nodosa and Boremys grandis. Arvinachelys, Neurankylus hutchisoni and Neurankylus utahensis have not been identified outside of the Kaiparowits Basin, but Denazinemys nodosa and Boremys grandis both are known from younger sediments of the San Juan Basin of New Mexico. Members of the genus Thescelus are known from the Campanian of New Mexico and the Maastrichtian of Wyoming, Montana and Saskatchewan, but are conspicuously absent in the Campanian of Alberta and Montana. The baenid assemblage in the Kaiparowits Formation provides support for both basin-scale endemism and north-south provincialism across Laramidia during the Campanian. There is also evidence for a latitudinal gradient in diversity, as only three baenid species have been reported from the temporally correlated Dinosaur Park Formation in Alberta.