New Mexico Geological Society Annual Spring Meeting
April 13, 2018

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The Trionychid Turtle axestemys Montinsana From the Paleocene Nacimiento Formation, San Juan Basin, New Mexico

Asher J Lichtig1 and Spencer G Lucas2

1New Mexico Museum of Natural History, 1801 Mountain Rd. NW, Albuquerque, NM, 87124,
2New Mexico Museum of Natural History and Science, 1801 Mountain Rd. NW

Axestemys montinsana is a trionychid turtle that was originally named and described from the Scarritt Quarry of the early Tiffanian interval of the Melville Formation in the Crazy Mountains Basin of Montana. We report the discovery of a skull attributable to this taxon from the Torrejonian interval of the Nacimiento Formation in Kutz Canyon, San Juan Basin, New Mexico. This identification of the first San Juan Basin record of Axestemys is based on comparison to the holotype skull, which compares closely with the New Mexican specimen. Thus, it is identified as an Axestemys based on its large (length) and triangular-shaped skull as well as the presence of a wide, smooth, unsculptured border of the carapacial callosity in an associated carapace fragment. The San Juan Basin and holotype specimens differ from other Axestemys in the extent of the parietals, with the frontal and postorbital broadly separating the parietals from the orbits. Furthermore, the anterior elongation of the cavum tympani in the New Mexican specimen is similar to the holotype of A. montinsana. This first New Mexican record of Axestemysmontinsana extends the known range of A. montinsana south from Colorado, resulting in a range covering the Rocky Mountain region from Montana to New Mexico. It also fits with models of little or no provinciality of vertebrates in the western USA during the Paleocene.

Referred specimen of Axistemys montinsana from the Nacimiento Formation in the San Juan Basin. Scale bar = 3 cm.
pp. 45

2018 New Mexico Geological Society Annual Spring Meeting
April 13, 2018, Macey Center, New Mexico Tech campus, Socorro, NM