Cuticular structure in Costacopluma mexicana Vega and Perrilliat, from the Difunta Group (Maastrichtian) of northeastern Mexico, and its paleoenvironmental implications

Abstract

Examination of extremely well-preserved cuticle samples from the Maastrichtian retroplumid crab, Costacopluma mexicana Vega and Perrilliat, collected in the Difunta Group in Nuevo León State, Mexico, documents the preservation of corpses in an anoxic microenvironment produced by decomposition of soft tissue of the organisms. All four cuticular layers, epicuticle, exocuticle, endocuticle, and membranous layer, as well as pore canals and tegumental glands, can be recognized. There is no evidence of resorption that accompanies molting. X-ray analysis of the cuticle indicates that the organic matrix was replaced by carbonate-hydroxyapatite, that the original calcitic material was replaced by quartz, and that the replacement proceeded from the outer and inner surfaces of the cuticle toward the interior. The specimens were interpreted to have been preserved in an organic-rich, restricted lagoon in which pH was changed by periodic influxes of fresh water.