Changing biodiversity of Mediterranean irregular echinoids from the Messinian to the Present-Day

International audienceMorphological and palaeoecological changes in irregular echinoid diversity during the Late Miocene Messinian stage have been analysed at the scale of the Sorbas Basin of southeast Spain. Biometrical and statistical analyses established the validity of species differentiation. An example is given for Messinian, Pliocene and Recent Schizaster species: S. saheliensis and S. canaliferus. Palaeoecological analyses show that irregular echinoid faunas record environmental changes, especially sea-level variations, with contrasting ecomorphological gradients for deepening and shallowing trends. Deepening is indicated by the stratigraphic succession of Clypeaster altus, associated Clypeaster marginatus^Spatangus^Schizaster and then Brissopsis species whereas shallowing is indicated by the opposite succession. The survival of Brissopsis, typically a stenohaline and relatively deep marine organism, in the marls interbedded within the uppermost Messinian gypsum of the Sorbas Basin testifies to the existence of marine connexions between this basin and other Mediterranean marine areas during the end of the evaporitic episode. Tabulation of irregular echinoid species diversity at eight time intervals between the Tortonian/Messinian boundary and the present-day (inclusive) for the Mediterranean Basin as a whole indicates a progressive increase in diversity from the latest Tortonian to the upper part of the pre-evaporitic Messinian before a fall in diversity during the salinity crisis. However, survivals after the crisis are very numerous, representing 78% of the maximum pre-evaporitic value