NEOHELICE (DECAPODA: BRACHYURA: VARUNIDAE) FROM THE MID-HOLOCENE, CANAL DE LAS ESCOBAS FORMATION NORTHEASTERN BUENOS AIRES, ARGENTINA

Neohelice granulata is an endemic, burrowing intertidal species of crab distributed in mudflats and saltmarshes of bays and lagoons along the coast, from southern Brazil to northern Patagonia (Argentina). It is widely known in modern population studies dealing with ecology, genetics, physiology, and burrowing. However, it is known in the fossil record only from the mid-Holocene of Buenos Aires, from deposits corresponding to the last marine transgression. The material comprises eleven almost complete specimens, six isolated carapaces and six isolated chelipeds, all preserved in micritic and sandy concretions of different shapes and sizes formed within their burrows. Diagenetic processes produced dorsoventral crushing of all of the specimens to different degrees but they are generally well preserved. No burrows were unambiguously identified, but the articulated nature of the exoskeleton suggests preservation within burrows. A winter kill might have been the cause of this assemblage, which also includes molluscs, cirripeds, and vertebrates. Herein, we describe in detail and for the first time this material from Parque Pereyra Iraola, Buenos Aires, Canal de las Escobas Formation, Destacamento Rio Salado Member, which includes a discussion on the taphonomy and paleoenvironmental implications of the assemblage.