The Tithonian ammonite fauna of the transect Cerro Lotena-Cerro Granito, Vaca Muerta Formation, Argentina. II. Family Simoceratidae

A new female specimen of the genus Volanoceras Geyssant, from the lower Zitteli Zone of the section Cerro Granito-I (southern Neuquén Basin, Argentina) is described as V. krantzense Cantú-Chapa. This specimen shows the sequence of ornamental stages (prosocline ribs with pseudo-furcations – periumbilical and ventrolateral tumid tubercles – periumbilical tubercles and ventrolateral clavi) as is known from the holotype (upper Zitteli Zone), but with slightly different timing and reaching a larger adult size. The large size and tumid sculpture of the present specimen are indicative of an early transient of the species, yet retaining these features closely similar to its ancestor Volanoceras aesinense (Meneghini). The male of the species from the Zitteli Zone of Pampa Tril is refigured, showing the expected complete identity of its phragmocone with that of the female at comparable diameter.