GONIODROMITES REUSS, 1858 (CRUSTACEA: DECAPODA: BRACHYURA: GONIODROMITIDAE): THE COCKROACH OF THE JURASSIC OCEANS

Goniodromites is perhaps the most common genus of crab thus far known from Jurassic deposits. Numerous Jurassic brachyuran genera and families are known, but Goniodromites is by far the most common in terms of number of localities at which it occurs and the number of individuals occurring at these localities. Twelve species have thus far been reported (Feldmann et al., 2006). The genus is most common in rocks of northern, central, and eastern Europe, but it has also been reported recently from Japan (Karasawa and Kato, 2007). Goniodromites has been recovered from coral-dominated, sponge-algal-dominated, and mixed biota bioherms as well as bedded limestones with no evidence of biological frameworks. Members of the genus have been recovered from localities from which few or no other decapod crustaceans have been collected, and they have been collected from almost every locality from which Jurassic brachyurans are known. Thus, it appears that the genus must have been eurytopic. Various morphological features of the carapace may demonstrate adapatations yielding a broad habitat preference. The orbits of Goniodromites are long and shallow, better developed than in many other groups within the Jurassic brachyurans, but quite different from the Homolidae and Homolodromiidae, for example, which had appeared by the Cretaceous. The dorsal carapace of Goniodromites spp. is unspecialized, lacking prominent spines or other ornamentation. The dorsal carapace regions of Goniodromites are weakly developed and include the main regions seen in almost all other brachyuran groups. The rostrum of Goniodromites is small and relatively unornamented, projects weakly beyond the orbits, and is much reduced compared to other Jurassic brachyurans. The genus demonstrates a reduction in the size and volume of the branchial regions compared to other Jurassic brachyurans, perhaps an adaptation to generally well-oxygenated environments. We believe that the relative lack of specialization within Goniodromites is what allowed it to thrive in a broad range of environmental conditions. It is also possible that the lack of specialization within the genus and indeed the family made them potentially ancestral to other brachyuran groups. Research supported by NSF EF-0531670 and INT-0313606 to Feldmann and Schweitzer.