DECAPOD CRUSTACEANS (BRACHYURA) FROM THE EOCENE TEPETATE FORMATION, BAJA CALIFORNIA SUR, MEXICO

Abstract

A large collection of brachyuran specimens from the middle Eocene Tepetate Formation, Baja California Sur, Mexico, has yielded sufficiently well-preserved specimens to provide revised descriptions and diagnoses for genera and species previously known from the area. Revised, more complete descriptions are given for Eriosachila bajaensis Schweitzer et al., 2002, and Lobonotus mexicanus Rathbun, 1930. A gone-placid specimen is questionably referred to Carcinoplax, which has a well-established Pacific record during the Miocene. All of the specimens of Amydrocarcinus dantei Schweitzer et al., 2002, thus far collected for which gender can be determined are males, suggesting that there may have been environmental or behavioral segregation of males and females of this species. Analysis of benthic and planktonic foraminiferans suggests that the Tepetate Formation was deposited in subtropical conditions, probably within the photic zone but below the seasonal thermocline, perhaps below 100–120 m. The age of the Tepetate Formation, according to larger foraminiferans, is middle Eocene, and according to planktonic foraminiferans is further constrained as upper middle Eocene (Bartonian). This age corresponds to the P14 foraminiferal zone based upon the Berggren et al. (1995) scheme and the E13 zone based upon the work of Berggren and Pearson (2005).