Uca maracoani (Crustacea, Decapoda, Ocypodidae) from a Miocene paleomangrove in Brazil: A case of evolutionary stasis among tropical American fiddler crabs

Abstract

The Miocene fiddler crab Uca maracoani antiqua Brito, 1972, from the Pirabas Formation (Brazil), has been recurrently claimed to be a valid species and the oldest fossil record of the brachyuran crab family Ocypodidae. However, morphological investigations with the aid of microCT scan images of a large number of topotypic specimens and re-examination of the type material of U. maracoani antiqua revealed that it should actually be merged into the synonymy of Uca (Acanthoplax) maracoani (Latreille, 1802). Therefore, U. maracoani, the morphology and ecological traits of which have persisted essentially unchanged for at least 16 Ma (Burdigalian to present), is actually a long-lived crab species inhabiting an estuarine, sheltered mudflat environment that, likewise, has essentially remained unchanged. Burgeoning evidence suggests that evolutionary stasis may not be uncommon among mangrove crabs, as revealed by Afruca tangeri (Eydoux, 1835) from the middle Miocene in northeastern Spain and U. ornata (Smith, 1870) from the Plio-Pleistocene in Honduras. Uca antiqua is redescribed and illustrated based on 3D volume reconstruction and several topotypic specimens. The microCT analysis revealed a considerable number of fossil concretions of U. maracoani, with both males and females likely sharing the same burrow. This is the first fossil record of a male fiddler crab with a female inside a burrow, where mating usually takes place. This mating style is common to almost all extant American fiddler crabs.