The prevalence of vestigial teeth in two beaked whale species from the North Atlantic

Abstract Beaked whales, Family Ziphiidae, occur in deep offshore and oceanic seas, where they are very difficult to study, so that much of our knowledge about them is derived from stranded animals. Most beaked whales (e.g., genera Mesoplodon and Ziphius) have only one pair of mandibular teeth. A reduced dentition is widely regarded as an adaptation to suction feeding, primarily on squid. However, vestigial maxillary and mandibular teeth have been recorded in some species. Here, we describe new records of vestigial teeth in 12 Sowerby’s beaked whales, Mesoplodon bidens, and one Cuvier’s beaked whale, Ziphius cavirostris, from a total 14 animals of these species, which stranded in 2019–2021 in Scotland. In nine M. bidens some tooth crowns were erupted and mild occlusal wear was visible, whereas pathological teeth were seen in ten individuals. The occurrence of vestigial teeth in Sowerby’s beaked whale appears to be significantly under-recorded, suggesting that vestigial teeth form as part of the normal development of the dentition. The reasons for the under-recording of the occurrence and the possible functionality of vestigial teeth in ziphiids are discussed.