Algunos aspectos de la problemática de la especie paleontológica: aplicación al caso de la diferenciación biométrica de Nassarius semistriatus (Brocchi, 1814) y N. elatus (Gould, 1845)

Abstract

The species problem in Paleontology is one of the most important; we must recognize the taphonomic events and after we must determine the fossil species as a second step in any paleobiologic or biostratigraphic study. Although analogic criteria exists for saying that a sample of fossils was derived from a population, fixed criteria do not exist in assigning a fossil population to a determined fossil species; the biospecies concept is, on the other hand, not applicable in Paleontology and this could lead to a new nominalism in the fossil species problem, but it is necessary to avoid that. We shall try to find some criteria- although indirect by and not very surely normally linked with the biospecies; we have selected from among them, for the present discussion, those related to the allometry (comparison of allometric curves) and the comparison of similar growth stages, because the growth is a basic character of the species, often modified after a taxonomic change. We have also used population dynamics (survivorship curve, which in similar environments are different for different species). We think that these procedures, associated with suitable statiscal background, can help us very much in discriminating species in Paleontology. The use of these concepts is exemplified by the differentiation of two fossil populations of Nassarius semistriatus and N. elatus from the Pliocene of the Empordà (Girona), species whose living representatives are recognized as true biospecies.