Past beaked whale diversity in the North Sea: reappraisal through a new Miocene record and biostratigraphic analyses

Extant beaked whales (family Ziphiidae) are deep diving suction feeders and none of them can be considered as a permanent resident of the shallow southern North Sea. The rich fossil record of ziphiids from Neogene deposits of this area is thus surprising. However, chronostratigraphic intervals of most recorded taxa remain poorly constrained, preventing from assessing the evolution of their local diversity. In this work, we describe a new ziphiid cranium from the Neogene of Antwerp (north of Belgium), which is attributed to Caviziphius aff. C. altirostris. Sediment samples were extracted from 15 fossil ziphiid cranial remains from this area (including the one described herein), referred to eight species. The samples were analysed for their palynological content, leading to improved chronostratigraphic ranges for several species. Seven to eight ziphiid species from the southern North Sea, all from the Messapicetus clade, are proposed to originate from a Serravallian to Tortonian (late Middle to early Late Miocene) interval, and three to six more precisely from the mid- to late Tortonian. Added to the fossil record of other regions, these results point to a Late Miocene radiation of members of the Messapicetus clade, possibly related to the synchronous worldwide decline of several hyper-longirostrine dolphin clades.