PALEOECOLOGY AND PRESERVATION STYLES OF K-T DECAPOD CRUSTACEA FROM THE DIFUNTA GROUP, NORTHEASTERN MEXICO

Cretaceous-Tertiary deltaic and inner shelf deposits from northeastern Mexico represent a variety of environments associated with evolution of local salt tectonism. Within these environments decapod crustaceans and other groups developed. Except for one specimen (Paleocene limestone and sandstone within the Difunta Group also include an incomplete crayfish), all crustacean species have been collected within Maastrichtian strata. Decapod species within these deposits consist of Costacopluma mexicana, Mascaranada difuntaensis, Sodakus mexicanus, and Mascaranada difuntaensis. Preservation is within phosphate, coarse sandstone, and/or calcareous nodules within a fine sandstone matrix. The most abundantly occurring crab is C. mexicana, a medium size crab, usually preserved as molts with one unique specimen found contained inside a gallery. C. mexicana has been collected from a variety of environments, usually associated with S. mexicanus, and rarely with M. difuntaensis. Cuticle structure of C. mexicana is peculiar, as epicuticle has a layer of cell-like structures. The second most abundantly occurring crab is D. australis, a relatively big, robust shore crawler crab. Sections of calcareous nodules containing D. australis depict unique lamination of exo and endocuticle with strange cell-like structures present on the thin epicuticle. S. mexicanus is a small and scarce crab always found with C. mexicana within inner shelf deposits. Lastly, M. difuntaensis, represented by only four complete specimens and found associated with large specimens of C. mexicana in shallow marine environments, is a swimming crab, possessing flattened fifth pereiopods. The Difunta group preserves a unique and scientifically important decapod crustacean assemblage due to its exquisite cuticle preservation of fossil crab occurrences during the KT boundary.