Nerodia undetermined

Nerodia sp. indet. Figure 12 Material. UNSM 139988 (24 pre-cloacal trunk vertebrae). Description. These trunk vertebrae are large in size and relatively wide when including the prezygapophyseal accessory processes, but are still relatively elongate along the centrum. The neural spines are tall and straight dorsally and somewhat undercut both anteriorly and posteriorly, but are rarely preserved in their entirety, hindering full comparisons between neural spine height and length. The neural arch is vaulted. The zygosphene is convex when viewed dorsally. The condyle and cotyle are round, and larger than the neural canal. The prezygapophyseal and postzygapophyseal facets are ovaloid in shape (sensu Holman, 2000) and oblique to the long axis of the centrum. The epizygapophyseal spines are absent. The subcentral ridges are pronounced and form deep grooves along the hypapophysis. The hypapophyses on each precaudal vertebra are well-developed, laterally compressed, directed posteriorly, and end in a somewhat pointed tip that extends posteriorly beyond the condylar head when complete. Remarks. The only other concurrent species during the Miocene is Nerodia hillmani and an indeterminate species from the Pratt Slide (Bw 123) locality, which is ~10.5-9.5 Ma (Clarendonian 3). Based on the larger size, longer hypapophysis, and longer prezygapophyseal articular facets, the Nerodia fossils described here are more similar to the unnamed Pratt Slide species than to N. hillmani. Comparison to more specimens, extant Nerodia sipedon and the somewhat younger Nerodia hibbardi from the Pliocene of Idaho and possibly Texas (Holman, 1968, 2000) may be necessary before assigning a species-level classification to these fossils.