Middle and Upper Devonian members of the phyllocarid order Archaeostraca Claus, 1888, are analyzed in both a phylogenetic and biogeographic context. Results of the phylogenetic analysis show that the suborders Ceratiocaridina Clarke inZittel, 1900, and Rhinocaridina Hall and Clarke, 1888, are paraphyletic as traditionally defined. The diagnoses of these suborders are revised and the use of the suborders Echinocaridina Clarke inZittel, 1900, and Pephricaridina Van Straelen, 1933, is proposed. Ceratiocaridina now contains the family Ceratiocarididae Salter, 1860; Rhinocaridina contains the family Rhinocarididae Hall and Clarke, 1888; Echinocaridina includes the families Aristozoidae Gürich, 1929, Ptychocarididae n. fam., and Echinocarididae Clarke inZittel, 1900; Pephricaridina includes the families Pephricarididae Van Straelen, 1933, and Ohiocarididae Rolfe, 1962. Generic definitions within the Rhinocarididae, in particular ”Rhinocaris” Clarke inHall and Clarke, 1888, are revised. The genus Echinocaris is redefined to include a monophyletic assemblage of species. Each of these clades is supported by several synapomorphies. Two new genera, Paraechinocaris and Carinatacaris, are proposed. Biogeographic analysis of this group reveals an extremely low rate of vicariant speciation, while episodes of range expansion are frequent. All occurrences of vicariance preceded the Late Devonian mass extinction. This may suggest a relationship between increased dispersal, diminished speciation, and the Late Devonian biotic crisis. Parallels between the Late Devonian mass extinction and the modern biodiversity crisis are suggested by the frequency of episodes of range expansion indicative of invasive species.

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