<i>Norisdelphis annakaensis</i>, A new Miocene delphinid from Japan

Two well-preserved delphinid crania have been recovered from the Haraichi Formation, Annaka Group, Gunma Prefecture, Japan (earliest late Miocene, Tortonian; 11.29–11.25 Ma). The specimens represent a new genus and species of delphinid, <i>Norisdelphis annakaensis</i>. The new species is characterized by transversely narrow and anteroposteriorly elongated external bony nares, and a wider proximal extremity of the left premaxilla. Phylogenetic analysis suggests that <i>Norisdelphis</i> is the most basal member of the Delphinidae. The previous oldest known described delphinid, <i>Eodelphinus kabatensis</i>, is from the upper Miocene (ca. 9 Ma), and other reliably dated and described fossil delphinids are no older than Pliocene; thus, <i>N. annakaensis</i> is the oldest convincingly dated and well-diagnosed fossil delphinid species yet described. <i>Norisdelphis annakaensis</i> expands the geological range of the family Delphinidae.