A large non-marine turtle from the Upper Cretaceous of Alabama and a review of North American "Macrobaenids".

The abundant record of marine turtles from the Late Cretaceous of Appalachia contrasts with the relatively poor record of contemporaneous terrestrial and freshwater species. A new taxon from the Santonian-Campanian of Alabama, Appalachemys ebersolei gen. et sp. nov., is described here and assigned to a grade of freshwater turtles known as "macrobaenids." Appalachemys can be differentiated from other "macrobaenids" by the presence of a nearly round carapace, deep nuchal emargination, and nine pairs of costals. With a carapace more than 80 cm in length, Appalachemys is among the largest freshwater turtles to ever inhabit North America. The absence of pre-Campanian "macrobaenids" from Laramidia indicates that the North American distribution of this grade may have been restricted to Appalachia prior to the recession of the Western Interior Seaway. Phylogenetic analysis places Appalachemys as the sister taxon to all post-Santonian "macrobaenids." Although the phylogeny lacks statistical support, it demonstrates morphological similarities between the K/Pg boundary species Osteopygis emarginatus and Maastrichtian-Danian species referred to Judithemys. We, therefore, refer all but the Campanian type species of Judithemys to the genus Osteopygis. A review of all North American "macrobaenid" occurrences reveals that despite originating in Asia, the record of the grade (as defined here) is predominantly North American. Future studies can test whether late Paleocene records in Asia and Europe resulted from dispersal from North America.