AN END-TRIASSIC SURVIVOR?: A POSSIBLE EUTHYCARCINOID ARTHROPOD FROM THE JURASSIC OF ARGENTINA

Euthycarcinoids are a distinctive group of arthropods with a phylogenetic relationship as a stem group on the myriapod lineage. Eighteen species have been identified, ranging from the Late Cambrian of Argentina to the Middle Triassic of France. Conventionally, euthycarcinoids are understood to have survived the end-Permian extinction and then succumbed to the end-Triassic extinction event. However, in this study, putative euthycarcinoid fossils have been identified from a lacustrine facies of the Middle Jurassic La Matilde Formation in Argentina (Patagonia). Seven euthycarcinoid specimens are preserved as carbonized impressions with a maximum length 16 mm and a corresponding width of 6 mm. The cephalic region it is not well preserved, and when it is present, it has two ?eyes located laterally on the head. Seven preabdominal somites are present; they are flattened, wider than long, with convex lateral margins. There are approximately six postabdominal somites which decreased in width posteriorly. This is the second record of a euthycarcinoid from Argentina and the first for La Matilde Formation. Given their absence from elsewhere, euthycarcinoids may have survived in South America as a relict group into the Jurassic.