High biodiversity in Polychelida crustaceans from the Jurassic La Voulte-sur-Rhône Lagerstätte

The Middle Jurassic La Voulte-sur-Rhône Lagerstätte preserves with remarkable details a highly diversified bathyal palaeocommunity dominated by arthropods. Polychelida Scholtz & Richter, 1995 are particularly abundant and are currently represented by Eryon ellipticus Van Straelen, 1923, Proeryon giganteus (Van Straelen, 1923), Hellerocaris falloti (Van Straelen, 1923), and Willemoesiocaris ovalis (Van Straelen, 1923). This new investigation reveals the presence of two new genera and three new species in this crustacean community: Voulteryon parvulus n. gen., n. sp., Cycleryon romani n. sp., which is the oldest occurrence of the genus, and Adamanteryon fourneti n. gen., n. sp., an enigmatic polychelidan of uncertain affinities. The genus Proeryon Beurlen, 1928 is also revised to solve problems of homonymy, and as a consequence we here propose the replacement name Proeryon zehentbaueri pro Proeryon giganteus Beurlen, 1930, non Proeryon giganteus (Van Straelen, 1923). These new results place the La Voulte polychelidan lobster community at the first rank in terms of familial and generic diversity (three families, seven genera) and at the second rank in terms of species diversity (seven species) just after the Late Jurassic Eichstätt Lagerstätte (eight species). Thanks to modern techniques, such as X-ray tomography, this study also documents structures never observed before such as thoracic appendages of Proeryon giganteus and Hellerocaris falloti. In the case of Hellerocaris falloti, these new observations suggest it is one of the closest fossil relatives to extant polychelids.