A new genus and species of trematopid amphibian from the Late Pennsylvanian of north-central New Mexico

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Abstract
A new genus and species of trematopid amphibian, Anconastes vesperus, is based on partial skeletons from the Cutler Formation of El Cobre Canyon, north-central New Mexico. Lithostratigraphic evidence is presented to demonstrate that the exposed stratigraphic section of the Cutler Formation in El Cobre Canyon spans the Permo-Pennsylvanian boundary, extending from at least Upper Pennsylvanian Virgilian to Lower Permian Wolfcampian. Indirect evidence indicates that the A. vesperus specimens were collected from what is believed to be a Virgilian horizon. This is the first trematopid to be reported from New Mexico and only the second from the Pennsylvanian. Many of the features that have been previously considered derived for the Trematopidae are reinterpreted as advanced states of trends within the family. Although this reduces the number of derived features that separates the trematopids from the dissorophids, it also reinforces the concept of a close relationship between the two families. In terms of the morphological trends within the family, A. vesperus appears to be considerably more primitive than the Early Permian forms. Well-ossified vertebrae, and very small, well-developed, sculptured osteoderms that formed a dense, non-overlapping, armor-like covering of at least the trunk region, indicate that A. vesperus was like the Early Permian trematopids in being adapted to a terrestrial existence.