COMBINING PALEONTOLOGICAL AND BIOLOGICAL CRITERIA WITHIN THE XANTHOIDEA (DECAPODA): TOWARD A NEW VIEW OF DECAPOD SYSTEMATICS, EVOLUTION, AND PALEOBIOGEOGRAPHY

Within the decapod crustaceans (shrimps, lobsters, and crabs), one of the most problematic groups for biologists and paleontologists is the Xanthoidea, a diverse group of "stone crabs." Many inhabit tropical and subtropical reefs, accounting for much of the current biodiversity among the crabs. This superfamily has been placed into one (Glaessner, 1969) to over 10 (Sakai, 1976) families or other subgroupings. DNA analyses, serology, spermatology, and cladistic analyses have begun to refine classification of extant forms; however, not all fossil xanthoids can be accommodated. Work underway by the authors combines biological and paleontological techniques to update and revise the fossil record of this important group by using dorsal carapace features as well as characteristics of the sternum, abdomen, chelae, and pereiopods as proxies for DNA, mouthparts, genitalia, eyes, gills, and antennae which are used by biologists and which do not typically fossilize. Classification and systematics of fossil crabs based upon hard part anatomy has been shown to closely approximate that based upon "soft parts" in other crab families (see Schweitzer and Feldmann, 2000 for example). Of the 9 or so currently recognized xanthoid families, 6 have been confidently recognized in the fossil record based upon hard part anatomy and 5 have been diagnosed based upon hard parts. The remaining xanthoid families are differentiated with difficulty when only hard parts are examined. Furthermore, several fossil genera that can be placed within the Xanthidae sensu lato cannot be accommodated in any known xanthoid family sensu stricto. Some, such as a new genus from Baja California, are clearly xanthoid but do not fit the current diagnosis for any recognized family. More importantly, many fossil taxa have hard part morphologies intermediate between the xanthoids and other, more primitive crab families such as the Portunidae. These crabs may be placed within one or more new families and may be related to the common ancestor of some of the more derived crab families. Recognition of new families that may have been ancestral to extant families will result in a much more comprehensive view of the evolutionary and paleobiogeographic history of the crabs. This work was supported by NSF grant INT 0003058 to Schweitzer and Feldmann.