EL GÉNERO LITHOTROCHUS CONRAD (GASTROPODA, VETIGASTROPODA) EN EL JURÁSICO TEMPRANO DE ARGENTINA

Abstract

The genus Lithotrochus (Gastropoda, Trochidae) is known in the Andean region from northern Peru to Argentine Patagonia, is endemic to this area and has a short time range (Sinemurian- Pliensbachian). Lithotrochus humboldtii (von Buch) is one of the first Mesozoic gastropod species described for South America. Almost all previous descriptions and figures seem to belong to the type species, for which there are at least two available names proposed by von Buch and d´Orbigny during the 19th century. A new species has been recognized from southern Neuquén Basin and is described here (Lithotrochus rothi n. sp.). The generic diagnosis is emended accordingly. Although the genus was found in several localities, its distribution is limited to sublittoral deposits, associated to a varied benthonic fauna, in the vicinity of coralliferous facies. A detailed analysis of the shell morphology of the type species and its ontogeny shows that there is a change in the traslation rate along the coiling axis as the shell grows, which could be related to a change in the organism life habits with time. These were probably grazing herbivores inhabiting firm substrates in well-lit and oxygenated waters. The presence of a smooth columellar lip points to links with the Trochidae s.l., but unfortunately their relationships are difficult to establish, since no protoconchs or opercula were found so far.