Cetopirus (Cirripedia: Coronulidae) from the lower Pleistocene of Salento (South Italy): evidence of an ancient right whale breeding ground in the Mediterranean?

The fragmentary fossil history of whale barnacles (Cirripedia: Coronulidae) is mainly constituted by remains of Coronula spp. (currently an endemic phoront of the balaenopterid Megaptera novaeangliae) in Plio-Pleistocene deposits sited along extant humpback whale migration routes, and especially in occurrence of breeding areas. We report the occurrence of a single plate of Cetopirus sp. nov. collected along with various remains of Coronula bifida in lower Pleistocene (upper Gelasian to lower Santernian) shelf deposits of Salento (South Italy). The Cetopirus specimen here studied (MSNUP I16903) was collected from a rocky cliff (known as "Il Fascio") outcropping inside the port of Otranto. The succession there exposed, which belongs to the Plio-Pleistocene Uggiano La Chiesa Formation, shows levels of marlstones alternating with calcarenitic layers. Main fossils are decapod crustacean and ichthyoliths; brachiopods, echinoids, bivalves, gastropods, corals, and turtles have also been recognized. Whale barnacles are known from three marly beds. The fossil here studied was found in the middle marly bed, where a rich assemblage of calcareous nannofossils allowed the dating to the Mediterranean Neogene Nannoplankton Zone MNN19a (1.95 to 1.73 Ma). MSNUP I16903 represents the most ancient occurrence of the genus Cetopirus, and the only one which predates the Late Glacial period. A comparison with the only known species of Cetopirus, the extant C. complanatus, reveals some anatomical differences (e.g., the presence in MSNUP I16903 of a thin radius and a peculiar structure of the transverse loops of the folded walls) which suggest that the Salento specimen belongs to a new fossil species. Cetopirus is currently known as an exclusive phoront of the right whale (Balaenidae: Eubalaena spp.), which inhabits the North Atlantic (as E. glacialis). The fossil distribution of Eubalaena spp. includes the Pliocene-Holocene of the Northeastern Atlantic coast and the Pliocene of Italy. The rich Italian Pliocene record of Balaenidae includes other two genera (Balaena and Balaenula) and also a neonate specimen; on the contrary, no right whales have been found in Italian Quaternary deposits. Since the high host specificity of whale barnacles is believed to date to the Pliocene, the presence of Cetopirus sp. nov., along with remains of Coronula bifida, in the lower Pleistocene beds of Otranto supports: (1) the permanence of Balaenidae in the Mediterranean during the early Pleistocene (as the Coronula bifida specimens do with regard to Balaenopteridae), despite the absence of Quaternary fossil balaenids and the lack of an extant Mediterranean population of right whales; (2) the existence of a baleen whale migratory route active between the central Mediterranean and the North Atlantic during the Plio-Pleistocene, since both balaenids and balaenopterids are now represented only by species that are to some extent migratory (moreover, Coronula bifida has been recorded - as Coronula barbara - in the early Pleistocene Red Cragg Formation of South England); (3) the utilization of the early Pleistocene shallow sea, covering the easternmost part of Salento, as a breeding area shared by Balaenidae and Balaenopteridae, thus evoking the sympatric distribution (a most unusual case among the extant mysticetes) which has been hypothesized for Eubalaena japonica and Megaptera novaeangliae with respect to some putative low-latitude winter grounds (e.g., the Hawaiian waters)