First records of extinct kentriodontid and squalodelphinid dolphins from the Upper Marine Molasse (Burdigalian age) of Switzerland and a reappraisal of the Swiss cetacean fauna

Abstract

The Swiss Upper Marine Molasse (OMM) documents a transgression event dated to around 21 to 17 million years in which dolphin and other vertebrate remains have been reported. We revised the whole cetacean (whales and dolphins) OMM assemblage available in main collections, focusing on the identification and interpretation of periotics (bone that contains the inner ear). Periotics are rare, but they provide the richest taxonomic information in the sample and hint to environmental associations. Micro-computerized tomography allowed the reconstruction of bony labyrinths for comparisons and environmental interpretations. Three families are represented by periotics: Kentriodontidae, Squalodelphinidae and Physeteridae. The cetacean taxonomic composition of the Swiss OMM reinforces biogeographical patterns reported for the Mediterranean and Paratethys during the Burdigalian at a regional scale and the Calvert cetacean fauna of the northwest Atlantic at oceanic scale.

Dawn of the Delphinidans: New Remains of Kentriodon from the Lower Miocene of Italy Shed Light on the Early Radiation of the Most Diverse Extant Cetacean Clade

“…In addition, several isolated Kentriodon-like ear bones are known from the Burdigalian deposits of the proto-Mediterranean area as well as from the nearby Paratethys, including the periotics referred to cf. Kentriodon from the Upper Marine Molasse (21-17 Ma) of Switzerland [92] and the ear bones referred to Kentriodontidae indet. from the Pietra da Cantoni Group (19-16 Ma) of northwestern Italy [93].…”

“…NBHF echolocation is currently used by several small-sized odontocetes (mostly delphinidan species) as a possible strategy to escape acoustic detection by large marine predators such as killer whales [98]. Thus, the predatory pressure of Squalodon (a possible analog of the extant orca [1,99]) may have favored the emergence of this peculiar ability in Kentriodon, thus preluding to the key role of NBHF adaptations in the subsequent radiation of the small delphinoids (see Aguirre Fernandez et al [92] for a similar hypothesis). As a matter of fact, Squalodon is common in the Libàno Sandstone as well as in the oldest strata of the Calvert Formation (note that the giant species Squalodon whithmorei reached 5.5 m in total body length [100]).…”