“Enantiopods”

Abstract

AbstractThe fossil arthropods discussed in this chapter represent problem taxa. Almost all occur in the middle of the Paleozoic (mostly Devonian), although one species derives from the Cambrian. All possess “long bodies” but present confusing and incomplete preservations of their anterior-most features. Their trunk limbs appear as unremarkable, either biramous or multiramous. These species often are placed among “primitive” arthropods, and such might well be so. Pancrustacea were long thought to have begun their evolution in the Cambrian as long-bodied, homonomous marine creatures. However, the molecular sequence data “insists” living taxa that conform to the longer bodied morphotypes occur high up in the pancrustacean cladograms. Thus, long-bodied homonomy must express either some kind of atavistic throwback as an apomorphy or are part of a logical continuum from the short-bodied Oligostraca, through middle-sized Multicrustacea, to the derived, long-thorax Allotriocarida. This chapter examines nine species, suggests alternative interpretations of their anatomy, and offers a dendrogram that could explain the evolution of Allotriocarida. “Enantiopod” is used as a catchall term—a common name—which is at best a parataxon.