Isopod crustacean fossils from the Cenomanian stratotype: five new species in suborders Cymothoida, Asellota and Valvifera

We report on a significant fossil collection of five isopod crustaceans that belong to five families from three suborders. These fossils were discovered in Le Mans (western part of Paris Basin, France) during the second half of the nineteenth century by the French paleontologist Edouard Guéranger. The historical quarry has been studied a few years before by the French paleontologist Alcide d’Orbigny and used as part of his Cenomanian stratotype (Leach, 1814). The collection consists of two species in the Cymothooidea Dana, 1852 (Cirolanidae Dana, 1852; Lantoceramiidae fam. nov.), two Valvifera G. O. Sars, 1883 (Chaetiliidae Dana, 1853; Idoteidae Samouelle, 1819) and one Asellota Latreille, 1802 (Stenetriidae Hansen, 1905), which were previously unknown from Upper Cretaceous strata as old as the Cenomanian age (roughly 93–99 ma). Although phylogenetic dating based on extant taxa has assigned Permian to Triassic age of origin for the Asellota, the Stenetriidae Hansen, 1905 specimen is the first fossil record for this family. Another asellotan, Fornicaris calligarisi Wilson and Selden, 2016, is known from the Triassic (Norian) dating from approximately 210–215 ma. The valviferans were unknown from Mesozoic strata, previously being found in the Oligocene of Romania and the Fur Formation, Upper Paleocene/Lowermost Eocene of Denmark (Polz, 2007). This diverse assemblage of fossils with taxa assignable to extant families and one new family provides evidence for the presence of a substantially modern isopod fauna as early as the Cenomanian.