Baleen whales (mysticetes) diverged from toothed whales and dolphins around 36 Ma. Among the oldest fossils attesting to their origin is Llanocetus denticrenatus from the Eocene (ca. 34 Ma) of Seymour Island, Antarctica. Isolated teeth from the same area suggest the presence of a second, potentially much larger species, but no further material of either form has been found to date. Here, we report the first record of Llanocetus outside Antarctica, based on a fragmentary but highly diagnostic tooth from Chatham Island, New Zealand. The new find considerably broadens both the geographical and the latitudinal range of the genus and suggests caution in interpreting the interrelationships of the basalmost mysticetes.

Felix G. Marx [felix.marx@tepapa.govt.nz; ORCID: https://orcid.org/0000-0002-1029-4001], Museum of New Zealand Te Papa Tongarewa, Wellington, New Zealand; Department of Geology, Museum of New Zealand Te Papa Tongarewa, 55 Cable Street, Wellington 6011, New Zealand. Hamish J. Campbell [h.campbell@gns.cri.nz; ORCID: https://orcid.org/0000-0002-6845-0126], New Zealand Institute of Earth Sciences (formerly Institute of Geological and Nuclear Sciences), 1 Fairway Drive, Avalon, Lower Hutt 5011, New Zealand.