New Mexico Geological Society Annual Spring Meeting — Abstracts

The Upper Cretaceous (Campanian) Menefee Formation is a dominantly nonmarine formation, which contains a wide variety of incomplete turtle fossils, including remains of adocids, trionychids, baenids, bothremydids, and the solemydid turtle Naomichelys. Two specimens of Denazinemys and one refered to aff. Denazinemys have been recovered from the Menefee Formation. Additionally, mixed in are five pieces that appear to be from a turtle pelvic girdle. These may represent the first girdle material associated with a specimen of Denazinemys. Additional indeterminate baenid specimens include specimen NMMNH [NM Museum of Natural History] P-70340, which includes two large pieces of the lateral edge of the anterior plastral lobe. The one specimen of the solemydid turtle Naomichelys is a small, ~4 cm diameter piece of turtle shell bone with the characteristic pattern of raised circles seen in this genus. This represents the only record of Naomichelys from New Mexico. Trionychids in the Menefee Formation are represented by a variety of shell fragments. One nearly complete costal, likely between the 3^rd and 5^th, has been collected (NMMNH P-25053). Additional trionychid specimens, including NMMNH P-70339 and P-70336, are recognized based on their characteristic surface pattern. The largest of the fragments clearly show the plywood structure discussed by Scheyer et al. in 2007. Pelomedusids in the Menefee Formation are represented by one specimen that includes a ~70% complete plastron and associated carapace fragments, CHCU [Chaco Culture National Historical Park] 81269, referred to the bothremyid, Elochelys cf. E. perfecta. This plastron is missing the anterior lobe, and the specimen is heavily weathered. The femoral-anal sulcus meets the medial sulcus at an “S”-shaped juncture in the center of the abdominal lobe. The two sulci are indistinguishable for ~1 cm. The placement of the hypo-xiphoplastral suture and the pattern of the sulci are similar to that seen on bothremydid turtles. In the middle portion of the plastron the sutures surrounding the narrow mesoplastron show a pattern that is diagnostic of bothremydid turtles. In addition to the plastron, parts of two sutured costals and one incomplete nuchal are present. The nuchal bone is nearly flat, with the anterior left edge of the carapace preserved. The medial edge of the preserved portion includes a cervical scute with a teardrop shape that comes to a point just beyond the right edge of the fragment. The sulci on the posterior lobe of the plastron are similar to those seen on Chedighaii and Elochelys in the “S”-shaped meeting of the midline and femoral-anal sulcus. The preserved portions of E. perfecta are largely consistent with what is found on this new specimen. This is the oldest bothremydid turtle in New Mexico and only the second specimen known from New Mexico. Diverse, and arguably understudied, Cretaceous turtle faunas exist outside the San Juan Basin in New Mexico. The turtle assemblage of the Menefee Formation is the second most diverse after the Fruitland and Kirtland formations in New Mexico. Diversity of turtles in the nonmarine strata of New Mexico mirrors the collecting effort expended on these units.