Modern echinoderms —invertebrates such as brittlestars and sea urchins — live only in open seas, but fossils from Europe suggest that this has not always been the case.

A team led by Mariusz Salamon of the University of Silesia, Poland, examined fossils of the Aspiduriella similis brittlestar from a quarry in southern Poland. The fossils were embedded in limestone dated to the Middle Triassic period, more than 240 million years ago. Minerals and geological structures within the rocks suggest that the fossils formed in conditions with very high salt levels, such as those present in hypersaline coastal waters. Few other fossils were found in the rock, also pointing to harsh living conditions. Echinoderm fossils have been used as indicators of open marine environments, something the authors caution against.

PLoS ONE 7, e49798 (2012)