Parastacid (Decapoda, Parastacidae) fossil mandible remains from the Early Miocene, New Zealand

The fossil record of freshwater crayfish (infraorder Astacidea) is surprisingly sparse, comprising mostly trace fossils, some body fossils and rarely biogastroliths. The cephalic molar ridge on mandibles of the Gondwanan parastacids (Parastacidae) has a hard robust apatite layer that may well facilitate fossilization. We report the first identification of fossil freshwater crayfish based on fragments of the molar ridge from their mandibles. Eight fossil fragments from the Early Miocene, St Bathans Fauna of New Zealand have divergent morphologies suggesting, minimally, three species-level taxa are represented. All have a ridged cephalic molar field unlike the two extant species of Paranephrops in New Zealand, but similar to other parastacids across the Southern Hemisphere. Overall, the fossil New Zealand material is more similar to extant Australian and South American species than Madagascan forms. Furthermore, it reveals a greater Early Miocene sympatric diversity (minimally three species) than in the extant New Zealand fauna, where only one occurs in a region.