New Eocene Decapods (Thalassinidea and Brachyura) from Southern California

A new decapod fauna has been recovered from Eocene rocks of San Diego County, Califomia. Decapod faunas of Eocene age have been rare from Califomia, although they are well described from the northern Pacific coast. Three new species, including Ncocallichirus rhinos, Ctenocheles secrctanae, and Minohellenus inexpressus, and two new genera and species, Acanthoportwms huchaiumi and Vegarfhron Santiago, are reported from this new fauna. A new genus has been erected to accommodate Portuniles triangulum and Portuniles granulifer; both are herein referred to Maeandricainpus, new genus. Callianassa matsoni Rathbun has been reassigned to Neocallichirus. Portions of the cephalothorax and abdomen of a species of Ctenocheles are described from fossils for the first time. Orhitoplax weaveri, previously known from Eocene rocks of Califomia and Oregon, is reported from the Eocene Mission Valley Formation and the Ardath Shale for the first time. In addition, one specimen of a stomatopod of indeterminate genus is noted. The Eocene decapod fauna from Califomia, now containing eighteen genera, has elements common to the northern Pacific coast of North America as well as taxa known only from Califomia; thus, the area appears to have been suited for decapods adapted to a wide variety of temperature and other environmental conditions. Several genera appear to have evolved within the region, whereas others may have been introduced from the Atlantic or Tethys region via the Central American Seaway. The number of Pacific amphitropical genera continues to increase; two portunid genera discussed here display such a pattern, adding to the four already reported for Cretaceous and Tertiary rocks of the region. Fossil decapod crustacean faunas have been well described from the Pacific Northwest of North America (see Schweitzer, 2001, for summary) and from Baja Califomia (Rathbun, 1930; Squires and Demetrion, 1992; Schweitzer et al., in press); however. Eocene decapods from Califomia have been relatively uncommon. Isolated occurrences of decapods have previously been described from Califomia (Rathbun, 1926, 1932; Squires, 1980, 2001; Bishop, 1988; Tucker et al, 1994). The discrepancy between numbers of Eocene occurrences in Califomia as opposed to areas to the north of that state was speculated to have been a result either of the paucity of Eocene rocks in Califomia or of differential evolutionary rates in the two areas (Schweitzer, 2001). It now appears that as new material is collected and made available for study, the Eocene record will become increasingly robust. The fauna described here is significant because it is one of the few Eocene decapod faunas known from the Califomia coast and brings to at least eighteen the total number of decapod genera now known from the Eocene of Califomia. The new material described in this report includes two new genera that appear to be endemic to the region as well as a new species of a genus not previously known from the Eocene of the west coast of North America. Further, three species are described here that are referable to genera already well-known from Tertiary rocks of the northern Pacific coast of North America. This mixture of taxa known only to the southern Pacific coast with taxa previously reported from farther north suggests that the Califomia coast was a region where taxa from the cooler northern provinces mixed with taxa derived from tropical regions to the south. OCCURRENCE OF FOSSILS A summary of locality information may be found in Table 1. The specimens described here from Localities 4572, 4573, and 4109 were collected from member B of the Santiago Formation of early Uintan (middle Eocene) age (Golz and Lillegraven, 1977). The Santiago Formation is composed of approximately 600 m of yellow sandstone underlying the Sespe and Vaqueros formations and overlying the Silverado Formation (Schoelihammer et al., 1981). The contacts with the underlying and overlying units are in