A new squalodelphinid species with a domed supraorbital process from the lower Miocene of New Zealand

Abstract

The extinct squalodelphinids are known from the Early to Middle Miocene of the north and south Atlantic (e.g., France, Italy, U.S.A., and Argentina) and the eastern and western Pacific (e.g., Peru, U.S.A., and Japan). Squalodelphinids are closely related to the extant Ganges and Indus River dolphins. These species have a set of two large and pneumatized crests on the dorsal surface of the skull above the orbit, referred to as the “supraorbital crests.” A new fossil dolphin from the Mount Harris Formation (Early Miocene, about 21.7–15.9 Ma) in North Otago, New Zealand is here identified as a member of the Squalodelphinidae that represents a new genus and species: Fordycetus taitonga. The estimated body length on holotype of F. taitonga is about 2.7 m long; it has a domed supraorbital process formed primarily by the maxilla, anteroposteriorly very short frontals at the vertex of the skull, and a deep and small orbital lobe of the pterygoid sinus. Fordycetus taitonga is the first squalodelphinid from New Zealand and the southwestern Pacific. Recently described Miodelphinus miensis from the northwestern Pacific was the first named member of the Squalodelphinidae from Japan and exhibits a weakly swollen, domed supraorbital process. These new members reveal early morphological disparity of the supraorbital process of the Squalodelphinidae during the Early Miocene. We also discuss the frontal opening of the maxilla—an exposure of the maxilla on the frontal roof of the temporal fossa—and a similar exposure among the Odontoceti, albeit via different configurations of bones and conditions.