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.

在日本群马县安中集团的原一队中，发现了两个保存完好的飞燕草cr（最早的晚新世是Tortonian； 11.29-11.25 Ma）。标本代表了新的属和新物种的飞燕草，Norisdelphis annakaensis。新物种的特征是横向狭窄且前后拉长的外部骨孔和左前上颌的较宽的近端。系统发育分析表明，夜蛾属是德尔菲科的最基础成员。先前已知的最古老的飞燕草Eodelphinus kabatensis来自中新世（约9 Ma），其他可靠地注明日期和描述的化石飞燕草都没有上新世。因此，安纳卡斯猪笼草是迄今已被描述的最古老的令人信服的日期和经过良好诊断的化石飞燕草物种。诺卡氏菌（Norisdelphis annakaensis）扩大了Delphinidae科的地质范围。