Search for: All records

Abstract Hutchemys rememdiumis a poorly understood softshell turtle (Trionychidae) from the mid Paleocene of the Williston Basin of North America previously known only from postcranial remains. A particularly rich collection of previously undescribed material from the Tiffanian 4 North American Land Mammal Age (NALMA) of North Dakota is here presented consisting of numerous shells that document new variation, some non-shell postcrania, and cranial remains, which are described based on 3D models extracted from micro-CT data. Although the observed shell variation weakens previously noted differences with the younger speciesHutchemys arctochelysfrom the Clarkforkian NALMA, the two taxa are still recognized as distinct. Parsimony and Bayesian phylogenetic analyses reaffirm the previously challenged placement ofHutchemys rememdiumwithin the cladePlastomenidae, mostly based on novel observations of cranial characters made possible by the new material and the micro-CT data. The new topology supports the notion that the well-ossified plastron of plastomenids originated twice in parallel near the Cretaceous/Paleogene boundary, once in theHutchemyslineage and once in theGilmoremys/Plastomenuslineage.Hutchemys rememdiumis notable for being the only documented species of trionychid in the mid Paleocene of the Williston Basin. The presence of multiple individuals in a carbonaceous claystone indicates this taxon lived in swamps and lakes and its expanded triturating surface suggests it had a durophagous diet.