New Mexico Geological Society Annual Spring Meeting — Abstracts

The middle Rio Puerco Valley in Bernalillo County, NM contains a thick succession of sediments deposited in and along the western margin of the Late Cretaceous Interior Seaway. Many of the sediments are fossiliferous and well exposed throughout the valley, and some strata contain numerous shark teeth. The upper part of the intertongued DakotaI Mancos succession is one such interval. These sediments have yielded well preserved ammonite and other invertebrate faunas, but till now no selachian remains. NMMNH locality 4517 is in the Clay Mesa Member of the Mancos Formation, a unit with an ammonite fauna that establishes its age as middle Cenomanian. This locality is unique because it represents the oldest Late Cretaceous shark fauna reported in New Mexico as well as the oldest occurrence of Ptychodus whipplei. Teeth of P. whipplei from NMMNH locality 4517 can be distinguished from teeth of P. anonymus Williston by their size and the shape of the cusp. Thus, the P. whipplei teeth from this site have a tall, nipple-shaped cusp, the cusp shape is cylindrical, and the angle between the cusp and the basal occlusal surface is approximately 90°. In contrast, the teeth of P. anonymus have a more conical lower cusp, the height of the cusp is roughly equal to the diameter of the cusp, and the angle between the basal occlusal surface and the cusp exceeds 90°. All of the characteristics of the teeth from this site are very similar to those of the teeth of P. whipplei. This site thus extends the range of P. whipplei from the Turonian back to the middle Cenomanian.