A new collection of fossil decapod crustaceans from the Cretaceous Rosario Formation, the Eocene Tepetate Formation and the Oligocene El Cien Formation, Baja California Sur, Mexico, has yielded two new genera and several new species, Amydrocarcinus dantei n. gen. and sp., Levicyclus tepetate n. gen. and sp., Eriosachila bajaensis n. sp., Oregonia spinifera n. sp., Archaeopus mexicanus n. sp., and Necronectes nodosa n. sp. Additionally, new occurrences of the previously described Lophoranina bishopi, Xandaros sternbergi, Icriocarcinus xestos, and Lobonotus mexicanus as well as Dardanus cf. D. mexicanus are reported. As part of ongoing work on global evolutionary and paleobiogeographic patterns within the Decapoda, the work has prompted a review and synthesis of decapod occurrences in the tropical and subtropical Americas including the southern United States, the Caribbean, Mexico, Central America, and northern South America. As a result of the systematic review, several new combinations are reported herein which include Eriosachila bartholomaeensis (Rathbun, 1919), Lobonotus sandersi (Blow and Manning, 1996; 1998), and Matutites americanus (Rathbun, 1935). Icriocarcinus is transferred to the Goneplacidae, extending the range of that family into the Cretaceous. Most Cretaceous through Miocene tropical and subtropical American taxa appear to have originated within the area and a large number were endemic. Most of the immigrants to the central Americas appear to have evolved along North Atlantic shelves and subsequently dispersed to the Americas, probably via continental shelf routes. In addition, as demonstrated by several previous studies, decapod crustaceans appear to have evolved in numerous middle- and high- latitude areas with subsequent dispersal to lower latitudes, contrary to the long held notion that the tropics are areas of origin with subsequent dispersal to other regions. Low-latitude decapod taxa tend to remain in low-latitude areas. The Maastrichtian and the Eocene appear to have been times of elevated extinctions within the Decapoda; however, the extinction patterns for those two time intervals are very complex.
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1 November 2002
NEW CRABS FROM THE EOCENE AND OLIGOCENE OF BAJA CALIFORNIA SUR, MEXICO AND AN ASSESSMENT OF THE EVOLUTIONARY AND PALEOBIOGEOGRAPHIC IMPLICATIONS OF MEXICAN FOSSIL DECAPODS
CARRIE E. SCHWEITZER,
RODNEY M. FELDMANN,
FRANCISCO J. VEGA