A Late Triassic Nuculanoid Clam (Bivalvia: Nuculanoidea): Implications for Luning Formation (Nevada, USA) Paleobathymetry

A silicified, thick-shelled, smooth-surfaced nuculanoid bivalve has been recovered by acid maceration of the Late Triassic (Carnian-Norian) strata of the Luning Formation, Nevada. Comparable modern nuculanoid clams inhabit water depths from 525-2,562 meters, and the living clam (an undescribed species of Pseudoneilonella from Caleta Sierra, Coquimbo, Chile) most similar to the fossil lives at 878-933 m. The Triassic nuculanoid clam (possibly a neilonellid) is inferred here to have inhabited marine waters at approximately 1000 m deep during deposition of the Shaly Limestone Member of the Luning Formation. This new fossil discovery falsifies hypotheses that the ichthyosaurs (Shonisaurus popularis) of Berlin-Ichthyosaur State Park, Nevada, USA, were deposited, respectively, in either shoreline deposits or in strata that accumulated above storm wave base.