The oldest fossil record of the extant genusBerardius(Odontoceti, Ziphiidae) from the Middle to Late Miocene boundary of the western North Pacific

Abstract

A new species of a beaked whale that belongs to the extant genus Berardius is described from the Middle to Late Miocene boundary age Tsurushi Formation ( ca 12.3–11.5 Ma) on the Sado Island, Niigata Prefecture, Japan. The new species, Berardius kobayashii sp. nov. represents the oldest record of this genus and provides a minimum age for the emergence of this extant genus. Berardius kobayashii sp. nov. has the following generic characters: the ratio between the width of the premaxillary crests and the width of the premaxillary sac fossae is 1.0–1.25, nodular frontals make isolated protuberance on the posterior part of the vertex. Among the species within the genus, B. kobayashii sp. nov. shares a unique character with B. minimus : the apices of the left and right hamular processes of the pterygoids contact medially, forming together a posteriorly directed medial point. In addition, B. kobayashii sp. nov. displays a unique combination of the following characters: it is extremely small in size, and the nasals are short, the ratio between the length of the medial suture of nasals on the vertex and the maximum width of nasals is less than 0.4. Berardius kobayashii sp. nov. fills the gap between the origin of the genus and later diversifications of the extant species. This discovery is also key to elucidate the process of the emergence and dispersal of the genus during the Middle to Late Miocene. Based on the distributional patterns of the fossil and extant species of the genus, the western North Pacific including the Sea of Japan may have been one of the areas for the evolution and radiation of this genus at the time before 11 Ma.

New data from the first discovered paleoparadoxiid (Desmostylia) specimen shed light into the morphological variation of the genus Neoparadoxia

“…Paleoparadoxiidae has an extensive and complicated taxonomic history, characterized by several changes in its nomenclature. This family was founded in 1923 8 , 9 with the discovery of two isolated teeth (likely belonging to two different individuals; see more below) from middle-late Miocene (late Serravallian to early Tortonian) marine strata of the Tsurushi Formation, on Sado Island, Niigata Prefecture, Japan (see 10 for age revisions to the Tsurushi Formation). These specimens (including a left second molar (m2) designated as the type) were originally identified as Cornwallius tabatai 8 ; however, they were both presumed destroyed in 1945 during the Second World War, with only Tokunaga's original photos and illustrations as reference material.…”

New data from the first discovered paleoparadoxiid (Desmostylia) specimen shed light into the morphological variation of the genus Neoparadoxia

“…Paleoparadoxiidae has an extensive and complicated taxonomic history, characterized by several changes in its nomenclature. This family was founded in 1923 8,9 with the discovery of two isolated teeth (likely belonging to two different individuals; see more below) from middle-late Miocene (late Serravallian to early Tortonian) marine strata of the Tsurushi Formation, on Sado Island, Niigata Prefecture, Japan (see 10 for age revisions to the Tsurushi Formation). These specimens (including a left second molar (m2) designated as the type) were originally identi ed as Cornwalliustabatai 8 ; however, they were both presumed destroyed in 1945 during the Second World War, with only Tokunaga's original photos and illustrations as reference material.…”