Origin, early evolution and palaeoecology of Gymnopleura (Crustacea, Decapoda): Basal palaeocorystoid crabs from the Upper Jurassic-Lower Cretaceous of central Europe

Abstract

Recent fieldwork has yielded new decapod crustacean material from Upper Jurassic-lowest Cretaceous bioclastic limestones at Kotou.c quarry near.Stramberk (Moravia, northeastern Czech Republic). Two specimens in this lot can be ascribed to the superfamily Palaeocorystoidea and represent the oldest gymnopleuran crabs known to date. A new genus and species, Moravacarcinus stramberkensis, are here erected and assigned to a new subfamily, Moravacarcininae, to accommodate this basal necrocarcinid. Our re-examination of Late Jurassic primitive crabs from southern Germany has resulted in the discovery of another early member of this group, here referred to a new genus, Juranecrocarcinus, as J. angulosum (Wehner, 1988). These new finds demonstrate that palaeocorystoids originated within shallow-water, reefal settings in the Upper Jurassic reef belt across central and southern Europe. We hypothesise that members of basal necrocarcinid subfamilies (Paranecrocarcininae and Moravacarcininae subfam. nov.), and thus the Gymnopleura, were derived from a dynomeniform ancestor which adapted to and became modified for a burying mode of life. Possible candidates are, for instance, the goniodromitid genus Cycloprosopon L.orenthey, in L.orenthey and Beurlen, 1929 and the longodromitid genera Longodromites Patrulius, 1959 and Planoprosopon Schweitzer, Feldmann and Laz.ar, 2007. The evolutionary pathways and palaeogeographical history of Mesozoic gymnopleurans were markedly influenced by the planktonic revolution which considerably enriched deeper-marine clastic sediments with nutrients from the Late Jurassic onwards.