Aptian archaeoniscid isopod from the Araripe Basin supports Tethyan-linked dispersal into Gondwanan lacustrine...

A new genus and species of fossil isopod, Cicero spectabilis n. gen. n. sp. is described from the Early Cretaceous (Aptian) Nova Olinda Member of the Crato Formation, Araripe Sedimentary Basin, Ceará, northeastern Brazil. The holotype, preserved in laminated limestones, represents the first confirmed record of the family Archaeoniscidae within this stratigraphic unit and extends the previously known paleogeographic distribution of archaeoniscid-like isopods into Gondwana lacustrine settings. The new genus is distinguished from other taxa currently referred to Archaeoniscidae-Archaeoniscus, Ferreniscus and Codoisopus, by its broad, ovate body, distinctive antennular subdivision, and a fan-like caudal structure formed by birramous uropods with well-differentiated exopod and endopod, combined with a rounded subrectangular pleotelson bearing a row of posterior setae. The exceptional preservation of C. spectabilis n. gen. n. sp. enables a detailed assessment of functionally relevant characters and supports interpretation of a benthic lifestyle on soft, low-energy substrates. A conservative concept of the family and a combination of body, pleon-pleotelson and antennular features justifies the placement of Cicero n. gen. within this extinct sphaeromatidean lineage. Within this framework, the occurrence C. spectabilis n. gen. n. sp. in a stratified lacustrine system of the Araripe Basin, together with other Mesozoic archaeoniscid-like records, suggest that some lineages currently assigned to Archaeoniscidae were able to colonize a range of non-marine environments during the Early Cretaceous, while also underscoring the need for a comprehensive phylogenetic reassessment of the group.