The Early Pliocene fish fauna of the Rharb Basin in NW Morocco based on otoliths - a reservoir for remigration into the Mediterranean

Abstract

The coquina along the Oued Beth south of Dar bel Hamri near Sidi Slimane is known for its fossil-richness, but the stratigraphic position has long been debated for Late Miocene or Early Pliocene age. A review of fossils and samples taken during field work in the mid-70ies supports an Early Pliocene age. Recently, I described the rich otolith-based fish fauna from these rocks, which are positioned in a funnel-shaped embayment close to the Strait of Gibraltar ideally situated as a reservoir for remigration of biota into the Mediterranean following the Messinian Salinity Crisis. The analysis of the fish fauna revealed that: 1.- The diversification of the fish fauna is exceptionally high and dominated by otoliths from adult specimens, which probably indicates a high food supply at moderate depth on a middle to lower shelf position during the deposition of the coquina. 2.- The otolith-based fish fauna from the Early Pliocene of the Rharb Basin shows a good resemblance not only to the coeval fauna of the Mediterranean, but also exhibits a notable proportion of putative endemic species and species related to today’s tropical West African fauna. 3.- The faunal composition thus exhibits a unique character that is sufficiently different from known or deduced neighboring bioprovinces, and thus a “Maghrebian bioprovince” is proposed for the Early Pliocene NW African region. 4.- The faunal comparison between Early Pliocene Mediterranean and NW African fish fauna reveals few candidates for allopatric speciation and in situ survival in the Mediterranean.