EARLY DELPHINIDA (CETACEA, ODONTOCETI) FROM THE MIOCENE OF THE SOUTHERN NORTH SEA BASIN

The earliest delphinidans (Cetacea, Odontoceti, Delphinida) first appear in the fossil record in the upper Oligocene, but are predominantly known from the Miocene. During the excavation of a series of construction pits in Antwerp (northern Belgium), two fragmentary early delphinidan crania were collected from lower Middle Miocene deposits of the Antwerpen Member (Berchem Formation). Both specimens show strong morphological similarities to Brevirostrodelphis dividum, originally described from the Miocene Calvert Formation of the U.S. Atlantic Coastal Plain. They are here identified as Brevirostrodelphis aff. B. dividum and Brevirostrodelphis sp., representing the first unambiguous records of this genus from the eastern side of the North Atlantic. In addition, the historical type specimen of Phocaenopsis sheynensis, collected in the early 1860s in the Antwerp area, most likely from Lower to Middle Miocene strata, is here redescribed and its systematic status is reassessed. It is here re-identified as Kentriodon sp. due to its strong morphological similarities with Kentriodon pernix, another early delphinidan originally described from the Calvert Formation of the U.S. Atlantic Coastal Plain. This specimen thus represents the third description of cranial material of Kentriodon from the North Sea Basin and the fourth from the eastern side of the North Atlantic. Based on the preponderance of juvenile specimens preserved, the southern North Sea Basin is herein tentatively hypothesized to potentially have served as a nursing ground for, or was favoured by relatively young individuals for several early delphinidan taxa during the Miocene.