New early Jurassic decapod crustacean from Patagonia (Chubut province), Argentina

Abstract

A well preserved decapod specimen was found in early Toarcian deposits cropping out on the western slope of Meseta Catreleo, central Chubut province, Argentina. It is a nearly complete exoskeleton preserved in lateral view, slightly crushed, in fine-grained sandstones. The skeleton is mostly articulated, though some pieces are disarticulated or missing. Taphonomic features indicate a relatively rapid burial after death, with little or no transport. This specimen is here described as a new species of the genus Mecochirus Germar (Decapoda: Glypheoidea). Mecochirus robbianoi n. sp. is characterized by a very long, achelate, first pair of pereiopods with a narrow long, straight dactylus, a thin carapace ornamented by low tubercules, with a slightly oblique cervical groove and a short acute rostrum. The family Mecochiridae arose in the Triassic, but the group diversified during the Early Jurassic. Mecochirus had a wide geographical distribution and is known from Lower Jurassic to Upper Cretaceous deposits. The new record from Chubut is one of the oldest for the genus, the oldest for South America, and the first for Argentina, thus considerably extending the known distribution of the genus during the Early Jurassic.