Taxonomy,ecology, and palaeobiogeography ofGervilleioperna (Gervilleiognoma) aurita n. subgen. n.sp. (Bivalvia) from the Middle Jurassic of northern Chile

A conspicuous, new species of the bivalve genusGervilleioperna occurs in coarse-grained bioclastic limestones and mixed siliciclastic-carbonate sediments of nothern Chile between 27° and 29° 40′ S. It is assigned to the new subgenusGervilleiognoma [type species:Gervilleioperna (Gervilleiognoma) aurita n. sp.], which appears to be endemic to northern Chile. On the basis of associated ammonites, the stratigraphic distribution of the new species can be restricted to the Early Aaleman (Manflasensis Zone) and thus it is of biostratigraphic value. The reconstructed life habit was mainly semi-endobyssate, resting on the thickened umbonal and anterior parts of the lower valve; the slightly twisted plane of commissure is oriented in an oblique position with respect to the substrate surface. The palaeogeographic distribution of the genus is briefly discussed.