Morphology based cladistic analysis of Metanephrops:: The most diverse extant genus of clawed lobster (Nephropidae)

We performed the first cladistic analysis of Metanephrops, the most diverse extant genus of clawed lobster, using a morphology-based data matrix of all 20 species of Metanephrops and 35 cladistically informative characters, all external hard parts. Unweighted cladistic analysis corroborates previous studies that indicated that homoplasy is rampant in the evolution of clawed lobsters. Only 5 of the 68 synapornorphies identified by the analysis are unambiguous, unreversed synapomorphies. Recent species of Metanephrops have traditionally been divided (non-cladistically) into four morphology-based groups. Cladistic analyses support the traditional, arafurensis, Atlantic/binghami, and japonicus groupings; these groups are monophyletic. The thomsoni group is not supported by the cladogram. The (two) oldest known fossil Metanephrops species occur in Late Cretaceous, shallow marine rocks of the eastem/Atlantic side of the Antarctic Peninsula. The stratigraphic and geographic occurrences of these fossil species are the basis for the previously hypothesized, Late Cretaceous, southern high latitude origin of Metanephrops. Cladistic results corroborate that Metanephrops originated in the southern high latitudes. The cladistically most plesiomorphic single species, the recent M. challengeri, and the next most plesiontorphic species, the Late Cretaceous M. rossensis, are both known from the high southern latitudes. Likewise, the most plesiomorphic species group, the binghami group, is best known from the high southern latitudes.