Middle-Upper Permian stenuroid (Asterozoa, Stenuroidea) from Las Delicias Formation, Coahuila, Mexico, relict youngest record for the group

Abstract

The Palaeozoic marine faunas include several fossil taxa that occupy an ancestral phylogenetic position relative to the major extant animal groups, and thus inform about the early establishment of the modern biosphere. The Stenuroidea represent a moderately diverse Class of Palaeozoic echinoderms regarded as ancestors of Ophiurodea, whose extant representatives include brittle stars and basket stars. Although most of stenuroid diversity is known from a few exceptional mid-Palaeozoic deposits, the broader evolutionary history of these extinct organisms remains obscured by their scarcity in the rock record. Here, we report the occurrence of a stenuroid asterozoan from the Middle-Upper Permian (Wordian-Capitanian) Las Delicias Formation, in the Coahuila state of Mexico. The presence of multi-articulated virgal ossicles on the arms provides strong support for stenuroid affinities, and comparison with representatives of this group indicates similarities to Antiquaster, genus previously only known from the Middle Devonian Silica Formation of Ohio. The discovery of the specimen in Las Delicias Formation makes this the first Mexican stenuroid, and the stratigraphically youngest member of this distinctive group of echinoderms known to date, extending their chronostratigraphic range by more than 60 million years.