New fossil portunids from Washington, USA, and Argentina, and a re-evaluation of generic and family relationships within the Portunoidea Rafinesque, 1815 (Decapoda: Brachyura)

Abstract

New portunoid fossils from southern Argentina and from the west coast of North America permit the reevaluation of the generic and family relationships within the Portunoidea Rafinesque, 1815. It has previously been suggested that the Portunidae and the Geryonidae Colosi, 1923, are closely related families (Manning and Holthuis, 1989). The new fossils suggest that the Geryonidae may in fact be derived from a portunid progenitor,ProterocarcinusFeldmann, Casadío, Chirino-Gálvez, and Aguirre Urreta, 1995, through a process of peramorphosis in which juveniles of the geryonid speciesChaceon peruvianus(d'Orbigny, 1842) resemble adults ofProterocarcinus latus(Glaessner, 1933). Examination of several genera within the portunid subfamily Polybiinae Ortmann, 1893, includingImaizumilaKarasawa, 1993;Megokkosnew genus;MinohellenusKarasawa, 1990;PororariaGlaessner, 1980;PortunitesBell, 1858; andProterocarcinus,suggests that the subfamily had an amphitropical distribution early in its history. New taxa reported here includeMegokkosnew genus andPortunites nodosusnew species. New combinations includeChaceon peruvianus(d'Orbigny, 1842),Imaizumila araucana(Philippi, 1887),Megokkos alaskensis(Rathbun, 1926),Megokkos hexagonalis(Nagao, 1932),Megokkos macrospinus(Schweitzer, Feldmann, Tucker, and Berglund, 2000),Minohellenus triangulum(Rathbun, 1926), andProterocarcinus latus(Glaessner, 1933).