NEW EOCENE FOSSIL DECAPOD CRUSTACEANS FROM BAJA CALIFORNIA SUR, MEXICO: A TETHYAN LINK

Recent work in Baja California Sur, Mexico, has resulted in a very large collection of fossil decapod crustaceans from the Eocene Bateque and Tepetate Formations. Although decapods have previously been described from each of these units (Squires and Demetrion, 1992; Schweitzer et al., 2002), the new collection contains many previously undescribed taxa. Decapod families that upon preliminary analysis are represented in the new collection include the Calappidae, Callianassidae, Cancridae, Goneplacidae, Grapsidae, Paguridae sensu lato, Parthenopidae, Portunidae, Raninidae, and Trapeziidae. Other Eocene faunas from the west coast of North America, although well-documented (Schweitzer, 2001; Schweitzer et al., 2002; Schweitzer and Feldmann, 2002), are not as robust and diverse as the new collection from Baja California Sur. Thus, the decapods in the new collection have important evolutionary, paleoecological, and paleobiogeographic implications. The middle Eocene age of the rocks from which the decapods were collected will permit direct comparison with the robust middle Eocene faunas known from Hungary and Italy (Müller and Collins, 1991; De Angeli and Beschin, 2001) and will help elucidate the timing of, appearance of, and phylogenetic relationships among extant brachyuran groups. Preliminary analysis of the fossils suggests a stronger connection with the fauna of Tethyan Europe than has previously been demonstrated for coastal Mexico, the United States, and Canada. In addition, many of the Tethyan forms present in the new collection previously have been reported from carbonate reefs, whereas the new material was recovered from siliciclastic sediments. The new decapods were collected from rocks rich in other invertebrates as well as shark and ray teeth, which will help to provide a more complete snapshot of the paleoenvironment in which the decapods were living than is typically possible.