Upper Cretaceous Dimorphic Pachydiscid Ammonite 'Menuites' in the WesternInterior of the United States

摘要

Highly dimorphic pachydiscid ammonites are fairly abundant in Montana, SouthDakota, Wyoming, and Colorado, and a few specimens are known from Utah and New Mexico. Two chronologic species are recognized, each represented by small adults (microconchs) and large adults (macroconchs). Microconchs have been assigned to Menuites Spath, 1922, whereas macroconchs have usually been assigned to Anapachydiscus Yabe and Shimizu, 1926. Both forms are considered Menuites in the present report.