Nautilus taiwanus

Most of the Nautilus fossils in Taiwan were found in Nantou County. The first Nautilus fossil was recorded by Ichiro Hayasaka in 1936, which was found in the present-day Ganzilin, Guoxing Township Nantou County, and was considered to belong to the Miocene strata.[3]

In 2002, a Nautilus fossil from Shimen formation in Zhongliao Township in Nantou was classified as a new species Kummelonautilus taiwanum, but it was not clearly stated why it was diagnosed as the genus Kummelonautilus, nor was a species characters provided, but only mentioned their similarities in overall shell shape, arrangement of sutures, and position of the columella. However, these characteristics cannot completely distinguish the Kummelonautilus taiwanum from other nautilus groups.[1] In another study in 2005, the identification characteristics of the Kummelonautilus taiwanum were provided, but it still not mentioned the autapomorphy that distinguish the Taiwan Kummelonautilus taiwanum from other nautilus species.[4]

In 2022, a study re-examined the holotype and paratype, along with the new specimens found in the early Miocene Houdongkeng formation in Qiangou, Guoxing Township, Nantou County, Taiwan, suggesting that the Taiwan Kummelonautilus taiwanum belongs to the genus Nautilus. Further, as the morphological evolution of the cephalopod shell is more conservative based on the cephalopod shell. the authors also suggest that the nautilus fossils from the Indo-Pacific region should be grouped into one genus rather than separate genera. However, due to the lack or incomplete preservation of Neogene specimens of the genus Nautilus, there are currently no morphological characteristics that can distinguish the type specimen of Nautilus taiwanus from other Nautilus species in Miocene Indonesia, Australia and extant species. Therefore, authors suggests continuing to use “Nautilus taiwanus” as the provisional name for this species until further comparative studies are conducted to clarify the taxonomic status of this species.[2]

Nautilus taiwanus is considered to be the northernmost fossil record of the genus Nautilus in the Indo-Pacific region in the Neogene.[2] A hypothesis suggests that the regional extinction of nautilus in the Cenozoic was associated with the occurrence of Pinnipedia and cetaceans, and that the record of nautilus declined significantly or even disappeared after the occurrence of these marine mammals in some areas.[5]