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 Metanephrops species and 35 cladistically informative characters, all external hard parts. Unweighted cladistic analysis corroborates previous studies which indicated that homoplasy is rampant in the evolution of clawed lobsters. Recent Metanephrops species 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 eastern/Atlantic side of the Antarctic Peninsula. Their stratigraphic and geographic occurrences are the basis for the previously hypothesized, Late Cretaceous, southern high latitude origin of Metanephrops. Cladistic results neither oppose, nor fully support, that the oldest fossil species, M. rossensis, is morphologically most primitive. The Late Cretaceous M. rossensis, and the recent M. challengeri, are unresolved on the cladogram, and share the distinction of being the most primitive. Thus, cladistic analysis suggests two equally plausible “most primitive” alternatives, with the one (M. rossensis) being supported by stratigraphic occurrence. Both of the cladistically most primitive species (M. challengeri, M. rossensis), as well as the oldest fossil species (M. rossensis, M. jenkinsi), are known from – or near to – the Antarctic region. Therefore, an origin in the Antarctic region seems likely. We look forward to new information, especially from new fossil occurrences and from molecular studies, for testing and refining these hypotheses.