Plio-Pleistocene Mediterranean bathyal echinoids: evidence of adaptation to psychrospheric conditions and affinities with Atlantic assemblages

Palaeontological evidences of autochthonous deep-water echinoids are so rare that the well-preserved assemblage herein described from the Plio-Pleistocene of Capo Milazzo (NE Sicily) provide an important opportunity to investigate the biodiversity of the bathyal echinoids in the Mediterranean late Cenozoic. The low diversity fauna studied is dominated by Cidaris margaritifera, Histocidaris sicula and Stirechinus scillae, which are species closely related to Recent echinoids today confined to the western Atlantic deep bottoms. The echinoid assemblages of Capo Milazzo and of the Plio-Pleistocene Argille Azzurre Formation (Italy) share a number of species, most of which are known also from shallow water Plio-Pleistocene deposits and the presentday Mediterranean; C. margaritifera is the only strictly bathyal echinoid that occurs in both formations. The palaeoecological study of these echinoids indicates an epibenthic way of life on muddy bottoms, in deep waters with psychrospheric conditions. The following species from the Argille Azzurre are interpreted as strictly bathyal: Histocidaris rosaria, Schizaster braidensis and Schizaster ovatus (transferred into the genus Holanthus). The modern Mediterranean (impoverished) deep-water echinoid assemblage has north-eastern Atlantic affinities and, with the exception of Holanthus expergitus, all the Mediterranean species found at bathyal depth are eurybathic, as they live also in shelf settings. In contrast, the bathyal echinoids of Capo Milazzo show strongest affinities with strictly deep-water western Atlantic species, particularly those of the Caribbean area. They vanished from the Mediterranean during the Quaternary due to the loss of psychrospheric conditions. Based on the Punta Mazza section, dated by nannofossils and data from literature, their stratigraphic range at Capo Milazzo is late Piacenzian-Calabrian. Enrico Borghi, Società Reggiana di Scienze Naturali, Via Tosti, 1 42100 Reggio Emilia, Italy, e.borghi@corghi.com Vittorio Garilli (corresponding author), Paleosofia-APEMA Research & Educational Service, Via Alla Falconara 34 90136 Palermo, Italy, vittoriogarilli@apema.eu, vittorio.garilli@paleosofia.it Sergio Bonomo, Istituto per l’Ambiente Marino Costiero, Consiglio Nazionale delle Ricerche, Calata Porta di Massa, Interno Porto di Napoli, 80133 Naples, Italy, sergio.bonomo@cnr.it