Heterotopy and heterochrony in the palaeotaxodont bivalve Natasia boliviensis (Babin and Branisa) from the Early Ordovician of northwestern Argentina

in the last few years several contributions concerning heterochronic processes have been produced, but only few papers dealing on heterotopy have been published. material of natasia boliviensis (babin and branisa, 1987) from the early ordovician of northwestern argentina includes specimens at different growth stages, from smaller, juvenile individuals with taxodont dentition, to larger adult shells displaying actinodont dentition. ontogenetic development of dentition is tentatively interpreted as resulting from heterotopic changes from an unknown praenuculid ancestor, whereas changes in shell outline could be explained by mean of heterochrony.