New microconchiate Hybonoticeras from Mexico

Abstract

A diversified and previously unknown record of microconchiate Hybonoticeras is analysed on the basis of the material collected in sections sampled bed-by-bed in the Mexican Altiplano. Five new species are described and compared to species traditionally recorded from the uppermost Kimmeridgian and the lowermost Tithonian in Europe. A general trend to smoothing in Mexican and European species during the earliest Tithonian is outlined.