A new species of extinct trionychid from the Early Oligocene (Orellan–Whitneyan NALMA) Brule Formation of North Dakota, USA

Softshell turtles ( Pan-Trionychidae ) have a particularly rich fossil record in North America, but only a few fragmentary remains have previously been reported from the Oligocene. A review of the literature suggests that Trionyx punctiger and Trionyx leucopotamicus , two taxa previously linked to the Oligocene, should be considered nomen dubia. We report well-preserved trionychid remains from the Early Oligocene (Orellan–Whitneyan) Brule Formation of southwestern North Dakota, including a complete cranium, mandible, and three partial shells that represent a new species of apalonine, Rafetus lysoni . The new species resembles other large-bodied apalonines from the Cenozoic of North America in skull morphology but differs notably in the poor development of carapacial and plastral callosities.