New species of Miocene spider crabs from New Zealand, and a partial cladistic analysis of the genus Leptomithrax Miers, 1876 (Brachyura: Majidae)

Abstract

Two new species of Leptomithrax, L. elongatus n. sp. and L. garthi n. sp., are described from North Canterbury deposits of Miocene age. Associated fossils suggest that these crabs lived in a cool temperate, shallow shelf environment. They bring to six the number of fossil Leptomithrax species known from New Zealand, which still has five Recent representatives of this genus. In addition, nearby Australia has two fossil and six Recent species. In total there are now eight fossil (all restricted to Australasia) and 15 Recent species of Leptomithrax from the western Pacific. The relationships of the eight fossil Australasian species and eight Recent species from Australasia and Japan were investigated by applying cladistic methods to a set of carapace characters describing shape and ornamentation. Using this analysis we tested Jenkin's hypothesis about the phylogenetic relationships of the Australasian Leptomithrax species. Our cladistic analysis of a set of carapace characters describing shape and ornamentation recognises five major groupings within Leptomithrax: the “L. elegans” and the “L. griffini” are known only from the fossil record; and the “L. longimanus”, “L. tuberculatus”, and “L. longipes” clades are known from both fossil and Recent records. The primary branching events resulting in these clades occurred around the time of the Eocene‐Oligocene boundary.

Keywords:

• Crustacea
• Decapoda
• Brachyura
• Majidae
• Miocene
• new species
• cladistic analysis
• New Zealand