New bivalve genus from the Early Jurassic of Neuquén Basin, Argentina, and its bearing on the Cuspidariidae (Poromyida) fossil record

Abstract

The new endemic genus Neuquemya, from Pliensbachian depositsin west-central Argentina, is here described and tentatively referred to theCuspidariidae on account of its shell characters. The new species Neuquemya leanzaorum has a thin inflatedshell, rounded anteriorly and rostrateposteriorly, with narrow postero-dorsal gape and opisthogyrous umbones. Thehinge region bears small cardinal tubercles. The shell is ornamented bycommarginal (anterior) and radial (posterior) sculpture, while the rostrum issmooth. The general and detailed characters of the shell are thus verysimilar to those of living cuspidariids. Cuspidariids are extremely specializedbivalves with special features related to their carnivorous habit. Their fossilrecord is scarce and their phylogeny is poorly understood. Since a few key shell characters and all softbody features of the new genus are not available, the alternative possibilitythat his taxon may be instead a remarkable example of homoeomorphic shellcannot be dismissed. If actually a cuspidariid, Neuquemya becomes the oldest known member of the family about 100 Myrolder than the Late Cretaceous records unequivocally accepted, and supports theargument that the origin of the group is much older that its known fossilrecord. The possible relationships of the new genus with other poorly known Mesozoicgenera are discussed. Whilst septibranchs in general and cuspidariids inparticular are now conspicuous elements of deep-sea faunas, this new genusinhabited near-shore environments of the Neuquén Basin.