Revision of Piceoerpeton MESZOELY (Caudata: Scapherpetontidae) and description of a new species from the late Maastrichtian and ?early Paleocene of western North America

The scapherpetontid salamander Piceoerpeton is known from the latest Cretaceous to middle Paleogene of North America and was the last surviving member of that paedomorphic family. A suite of vertebral features differentiates Piceoerpeton from other scapherpetontids, including three atlantal features that are autapomorphic within the family: odontoid process reduced to an anteriorly short, nipple-like structure; ventral surface of odontoid process lacks an articular surface for contact with skull; and articular surfaces of anterior cotyles are deeply concave. Differences in inferred body size and vertebral structure permit the recognition of two congeners: P. willwoodense, a large-bodied species (estimated snout-vent length = 100 cm) from the late Paleocene of the Western Interior and early Eocene of the Canadian Arctic and the much smaller P. naylori new species from the late Maastrichtian and ?early Paleocene of Wyoming and Montana, USA. In terms of its older age, smaller size, and less derived vertebral features, P. naylori is potentially ancestral to P. willwoodense.