New Mexico Geological Society Annual Spring Meeting — Abstracts

Echinoid fossils are extremely rare in the Upper Cretaceous strata of the Western Interior, where fewer than 60 unique occurrences are known to date, most of them represented by only a few tests or isolated spines (Hook and Cobban, 2017). Five new echinoid specimens, belonging to the genus Mecaster, have recently been recovered from the Upper Cretaceous (Turonian) Prionocyclus hyatti Ammonite Zone, within the Semilla Sandstone Member of the Carlile Shale near Cabezon (NMMNH locality 13149) in the southeastern San Juan Basin of northwestern New Mexico. These New Mexican specimens compare well with Mecaster in having a small to medium sized test that is broad and tall relative to length, with an abrupt truncation in the rear and a slight to moderate sinus in the front. The ambulachral areas are moderately depressed, and the interambulachral spaces are prominent. These newly discovered echinoid specimens are the stratigraphically youngest record of Mecaster in New Mexico, as well as the first to be recorded from the Turonian of New Mexico. Further work with these specimens is needed to be able to assign them to a species.

References:

1. Hook, S.C., and Cobban, W.A., 2017, Mecaster batnensis (Coquand, 1862), a late Cenomanian echinoid from New Mexico, with a compilation of Late Cretaceous echinoid records in the Western Interior of the United States and Canada: Acta Geologica Polonica, v. 67, p. 1–30.