James W. HagadornR. Mark LeckieCollette, Joseph H.2024-04-262009-07-0820092009-0910.7275/891151https://hdl.handle.net/20.500.14394/46882Three new types of arthropod from Cambrian intertidal lithofacies of the Elk Mound Group and Lodi Member of Wisconsin, and the Potsdam Group of Quebec are described. These arthropods are preserved ventrally in three dimensions – allowing detailed characterization of morphology. Arenocaris inflata, from the Furongian Elk Mound Group and St. Lawrence Formation, is the earliest occurrence of a phyllocarid. Mosineia macnaughtoni, a large (>10 cm long) euthycarcinoid arthropod, also occurs in Elk Mound strata. Mictomerus melochevillensis represents a new family of early euthycarcinoids, and is a large (8–10+ cm long) arthropod with eleven pairs of homopodous, uniramous limbs. Phylogenetic analyses and reviews of Paleozoic phyllocarid systematics are presented, using morphology-based characters from Cambrian to Recent taxa. Resulting cladograms place Arenocaris inflata into a systematic context, and reveal that the families Ceratiocarididae and Caryocarididae, as traditionally defined, are paraphyletic. Caryocarididae is elevated to subordinal rank (Caryocaridina n. suborder), resulting in two monophyletic suborders. Emended diagnoses are integrated into this analysis, and result in synonymy of 30 Cambrian – Silurian caryocaridids and ceratiocaridids into 11 pre-existing species. The phyllocarid Arenocaris inflata from the Elk Mound Group of Wisconsin and the large enigmatic arthropod Mictomerus melochevillensis from The Potsdam Group of Quebec are both directly associated with trace fossils. Direct association between these arthropods and their traces allows functional morphological details of the animal to be assessed, provides a framework for understanding how arthropods can be sand-cast in three-dimensions, and helps provide insight about subaerially-produced traces from the Potsdam Group.PaleontologyeuthycarcinoidsphyllocaridsFurongianElk Mound GroupPotsdam GroupGeologyPaleobiologyPaleontologyGeologythesis