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, Norisdelphis annakaensis. 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 Norisdelphis is the most basal member of the Delphinidae. The previous oldest known described delphinid, Eodelphinus kabatensis, is from the upper Miocene (ca. 9 Ma), and other reliably dated and described fossil delphinids are no older than Pliocene; thus, N. annakaensis is the oldest convincingly dated and well-diagnosed fossil delphinid species yet described. Norisdelphis annakaensis expands the geological range of the family Delphinidae.

Suborder ODONTOCETI Flower, 1867 

Infraorder DELPHINIDA Muizon, 1984 

Superfamily DELPHINOIDEA Gray, 1821 

Family DELPHINIDAE Gray, 1821 

Etymology—From Greek, norís, meaning early, and delphis, dolphin. 

Etymology— Named for Annaka City, Gunma, Japan, where the holotype and the paratype were found.

Toshiyuki Kimura and Yoshikazu Hasegawa. 2020. Norisdelphis annakaensis, A New Miocene Delphinid from Japan. Journal of Vertebrate Paleontology. e1762628. DOI: 10.1080/02724634.2020.1762628