LEPIDORBITOIDES MINIMA DOUVILLÉ FROM MEXICO, A FORAMINIFERAL INDEX FOSSIL FOR THE CAMPANIAN

Mexican topotypes of Lepidorbitoides minima Douville, type species of the genus Orbitocyclina Vaughan 1929, exhibit an orbitoidiform architecture conditioned by an obliquely-overcrossed stolon system in only three stolon planes in the medium layer of the shell and arising from a single auxiliary chamberlet. This architecture is identical with the one observed in Campanian early species of the Tethyan genus Lepidorbitoides. Orbitocyclina is therefore placed in synonymy with Lepidorbitoides Silvestri, 1907. This opens the way for a transatlantic biozonation based on quantitative methods supported by evolutionary theory using nepionic acceleration as a measurable feature.