NEW TURTLE SPECIMENS FROM THE MORENO HILL AND MENEFEE FORMATIONS (TURONIAN-CAMPANIAN) OF NORTHWESTERN NEW MEXICO

Recent survey of Upper Cretaceous formations cropping out in Northwestern New Mexico have resulted in an increased understanding of turtle diversity and evolution within the Western Interior Basin. Significant new materials include partial carapace and plastron fragments from the Turnonian-aged Moreno Hill Formation, Zuni Basin, and a nearly complete carapace and plastron from the lower Campanian Menefee Formation, San Juan Basin. These formations were deposited during repeated regressive cycles of the Western Interior Seaway. During this time, this region of New Mexico was a swampy flood plain with slow meandering streams producing fluvial deposits of sandstones, mudstone, and coal.

Turtle shell fragments (NM-16-05-01-B2) from the Moreno Hill locality represent a large individual and range in size from 0.557 cm to 2.554 cm. Pronounced, elongated node-like ornamentation of the carapace suggests a close relationship to Denazinemys and/or Scabremys, and referral to Baenodda. Documentation of Baenodda from the Moreno Hill Formation would extend the published record of this clade at least 10 million years older than previously recorded.

The second turtle specimen (NM-17-05-21-D9) is a nearly complete turtle carapace and plastron from the Menefee formation. The cranialmost aspect and the left peripherals are damaged, with some damage occuring premortem. Due to extensive fusion, suture patterns on the shell could not be identified. The craniocaudal length of the carapace is at least 56 cm, whereas the transverse width is estimated at 61 cm. The smoothness of the carapace suggests that the specimen likely had a semi-aquatic lifestyle. The upward curvature of the peripherals, pores on the pleurals, as well as the smooth, dome-shape of the shell suggests a the specimen may be referable to Adocidae. However, the long and narrow plastron, and fusion of the carapace to the plastron are characteristics of baenids.