Specimen-Based Research Results in Recognition of AN Explosive Radiation of Jurassic Brachyura (Crustacea: Decapoda)

The prevailing notion of Jurassic decapod diversity and disparity had been that each is relatively low. Most Jurassic brachyurans (crabs) had been referred to three families in as many superfamilies (e.g., Glaessner, 1969). Several field seasons in Romania, and extensive work in many of the major museum and other collections in Germany, Austria, Poland, the Netherlands, Spain, and France suggests that Jurassic diversity and disparity at the family, genus, and species level is much higher than previously thought. Examination of previously underutilized features such as the orbital structures and lateral flanks has led to the recognition of, at this time, eleven families. Eleven new genera also have been named, and the work is far from complete. Interestingly, the amazingly large number of families and genera appears in the Late Jurassic and especially in the Tithonian, the latest Jurassic. Diversity of Jurassic brachyuran families and genera appears to have been much lower prior to this, with few brachyuran records in the Bathonian, Bajocian, and earlier times. Specimen-based and field-based research has also yielded remarkably detailed information on the paleoecology of these animals. The highest family, genus, and species level diversity occur in Jurassic coral reef environments, some yielding as many as 37 species in 27 genera. Reefs dominated by sponges yield significantly lower levels of diversity, with 4 species in 4 genera. We hypothesize that paleoenvironmental factors played a role in the rapid evolution of these animals. This major adaptive radiation in the evolutionary history of the Brachyura could not have been recognized by a search of the literature or a database. This research is supported by NSF grants EF-0531670 and INT-0313606 to Feldmann and Schweitzer.