1. Instituto de Geología y Minería, Universidad Nacional de Jujuy, Avenida Bolivia 1661, San Salvador de Jujuy (4600), Argentina
2. Australian Museum, 6 College Street, Sydney, NSW 2010, Australia
3. O'Higgins y Zarate, 108, Palpalá (4612), Jujuy, Argentina

Correspondence to: N. E. Vaccari¹ Email: evac@idgym.unju.edu.ar

Abstract

Euthycarcinoids are one of the most enigmatic arthropod groups, having been assigned to nearly all major clades of Arthropoda. Recent work has endorsed closest relationships with crustaceans¹ or a myriapod–hexapod assemblage², a basal position in the Euarthropoda³, or a placement in the Hexapoda⁴ or hexapod stem group⁵. Euthycarcinoids are known from 13 species ranging in age from Late Ordovician or Early Silurian to Middle Triassic, all in freshwater or brackish water environments⁶. Here we describe a euthycarcinoid from marine strata in Argentina dating from the latest Cambrian period, extending the group's record back as much as 50 million years. Despite its antiquity and marine occurrence, the Cambrian species demonstrates that morphological details were conserved in the transition to fresh water. Trackways in the same unit as the euthycarcinoid strengthen arguments that similar traces of subaerial origin from Cambro-Ordovician rocks were made by euthycarcinoids^{7, 8}. Large mandibles in euthycarcinoids^{6, 9} are confirmed by the Cambrian species. A morphology-based phylogeny resolves euthycarcinoids as stem-group Mandibulata, sister to the Myriapoda and Crustacea plus Hexapoda.

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