Miocene sponge assemblages

During the Miocene salinity crisis, changing environmental conditions, including a sharp reduction in water exchange between the Mediterranean and the Atlantic Ocean, changed the geographic ranges of many organisms. We investigated loose Miocene sponge spicules from a population then inhabiting the strait between the Mediterranean and the Atlantic Ocean. From the 18 recognized species, at least 8 still inhabit the area and others are recorded from closely located areas. Some have their closest relatives in Indo-Pacific waters and Japan today, the range of some populations may have shrunk after the closure of the Mediterranean Sea, with some sponge species surviving only in refugia.

The illustration shows spicules of Miocene sponges.