A relict Triassic brittle star (Echinodermata, Ophiuroidea) in Lower Jurassic strata of Asturias, north-west Spain

Abstract

Ophiuroids, also known as brittle stars, are an important component of modern marine benthos, yet their fossil record is still poorly understood. Here, we describe new finds of ophiuroids from the upper Sinemurian (Lower Jurassic) of Asturias, north-west Spain. The material consists of several articulated specimens that show all relevant anatomical details to allow for an exhaustive description of a new species, Arenorbis santameraensis sp. nov., which adds a Jurassic member to the genus Arenorbis previously known exclusively from the Middle Triassic of central Europe. We demonstrate that Arenorbis has characters that are typically found in the suborder Ophiodermatina. The new Jurassic record of Arenorbis shows remarkable parallels with its Middle Triassic equivalents in terms of sedimentological and taphonomic context, suggesting niche conservatism in this genus. In contrast to its wide geographical distribution during the Middle Triassic, the new species is currently only known from a restricted area, which suggests that it represents a Jurassic relict of a formerly widespread Triassic lineage.