B16
Helicoprion bessonowi
teeth of holocephalan that look like ammonoid shell

Helicoprion is spiral-tooth whorl that is mainly found from Early Permian strata. Since the first Helicoprion was found in 1886 and named in 1899, its function and form had been puzzled paleontologists. An external defensive structure and a feeding structure were two major hypotheses. A 2013 study that CT scanned the Helicoplion with surrounding endoskeletal elements revealed that Helicoprion is the lower jaw teeth of a Holocephali. The whorl occupied most of oral cavity, which bears no upper tooth. The closure of jaw rotates teeth posterodorsally that pushed the food posteriorly and sliced it. This specimen was found from the Asio Terrane of Gunma prefecture in 1897. Dr. Tadatsugu Kochibe, the head of the geological survey of Japan at that time, brought the photograph of this specimen to International Geological Congress at Russia to ask its classification, but nobody could answer. In 1898, a similar fossil was found from Russia and was named as Halicoprion in 1899 by Dr. Alexander Karpinsky, who sent the description to Dr. Kochibe. Then, in 1900, Mr. Eijiro Sagawa wrote a report of this specimen by referencing Karpinsky’s work to the Journal of Geography in Japanese and in 1903, Hisakatsu Yabe wrote the report in English. History of this specimen shows an active international interaction existed in the area of geology and paleontology before the end of 19th century.　(Tai Kubo)

References

Tapanila, L. et al. (2013) Jaws for a spiral tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion. Biology Letters 9: 20130057.

Yabe, H. (1903) On a Fusulina-limestone with Helicoprion in Japan. The Journal of the Geological Society of Japan 10: 1–13. 

佐川栄二郎（1900）「日本及ロシアに出でし最古魚類遺歯」『地学雑誌』12: 26–29。