New insights on ancient cetacean movement patterns from oxygen-isotope analyses of a Mediterranean Pleistocene whale barnacle

The fossil record of whale barnacles (Coronulidae) mostly consists of remains of Coronula in Plio-Pleistocene coastal deposits that have been interpreted as ancient mysticete breeding/calving areas. Based on such indirect evidence, it has been proposed that, during the early Pleistocene, the epeiric seas of southern Italy were utilized as winter grounds by baleen whales seasonally migrating to higher latitudes. In order to investigate this hypothetical scenario, here we provide the first oxygen-isotope profile obtained along the growth direction of a fossil coronulid shell; the analyzed specimen, referred to the extinct species Coronula bifida, was collected from early Pleistocene (latest Gelasian-earliest Calabrian) deposits of Apulia (southern Italy). The delta18 O series thus obtained is discussed in the light of two contrasting hypotheses: (1) the barnacle lived on a host that resided all-year-long in the Mediterranean; (2) the barnacle lived on a host that seasonally migrated towards high-latitude areas outside the Mediterranean. Based on several neontological and palaeontological lines of reasoning, as well as on chemical/physical data on the present-day global ocean, we argue that the analyzed barnacle was likely hosted on a migrating whale, which exploited the central Mediterranean as a breeding area in wintertime and moved towards the northeastern Atlantic feeding grounds in summertime. Therefore, the present study sheds further light on the seasonal movement patterns of the ancient baleen whales of the Mediterranean and evokes Plio-Pleistocene roots for the migratory habits of extant mysticetes, whose ultimate causes could be sought in the onset of the long-term Northern Hemisphere glaciation.