New Mexico Geological Society Annual Spring Meeting — Abstracts

We report here preservation of an extremely rare inoceramid bivalve color pattern in Cataceramus? glendivensis Walaszczyk, Cobban and Harries, 2001. This inoceramid was recovered from the upper part of the Baculites baculus Zone in the Pierre Shale of northeastern New Mexico. The locality (NMMNH L-12263) is in the upper Pierre, 80 km southwest of Raton near Cimarron, about 40 m below the base of the Trinidad Sandstone.

The very well preserved shell, which has both valves articulated, is large, prosocline, ventroposteriorly elongated, oblique to the long axis, and is equivalved and equilateral. The anterior margin is short, slightly convex, and passes into a long ventral margin. Most of the hinge line and posterior margin are missing. The valves are weakly inflated. The beak is curved anteriorly and projects slightly above the hinge line. Irregularly spaced, rounded rugae weaken ventrally. A fairly deep groove near the posterior end of the shell may be a sublethal, healed injury that caused a growth anomaly.

The color pattern consists of alternating dark and light radial bands of varied widths. These bands follow the course of the long axis of the shell. The color banding is best preserved in the umbonal region; starting at the growth axis, the bands are narrow, and bands of the same color are of relatively equal width. In a dorsal direction, the bands begin to widen, and the dorsal-most band is very wide. Also, the bands appear to expand in width ventrally.

This is the first report of a color pattern in Cataceramus? glendivensis. Inoceramid color patterns are extremely rare, and reports of them are scant.

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References:

1. Walaszczyk, I., Cobban, W. A. and Harries, P. J., 2001, Inoceramids and inoceramid biostratigraphy of the Campanian and Maastrichtian of the United States Western Interior Basin: Revue de Paléobiologie, v. 20, p. 117-234.