Helicoprion bessonowi

Overview

Helicoprion bessonowi is a cartilaginous fish with teeth coiled into a whorl. One unfamiliar fossil fragment prompted questions about the animal’s identity for a long time. Imagining this genus’s tooth row inside the lower jaw reveals a mouth unlike that of familiar fishes.^[1][3]

Key facts

Each row in the whorl consists of teeth rather than shell ornamentation. Studies of Helicoprion describe a tooth row with older teeth partly concealed, and the cartilage supporting it. The key is connecting a conspicuous fossil with the structure of the jaw.^[1]

Time and place

It is known from Early Permian fossils. The Early Permian spans approximately 300–270 million years ago. The University of Tokyo museum presents a specimen of this species from Midori, Gunma Prefecture, in present-day Japan.^[3]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

Its defining feature is a tightly coiled tooth row. Genus-level research describes the whorl inside the lower jaw and its supporting cartilage. The sizes and proportions of teeth arranged in a row are also used in studies distinguishing species.^[1][2]

A measurement table in a 2013 study records a height of 66.1 mm for one part of the tooth-whorl ring in the reference specimen TsNIGR 1/1865. This measurement must be distinguished from the diameter of the entire whorl or the animal’s body length.^[2]

Habitat and reproduction

How might such unusual teeth have been used to process food? Rather than examining the whorl alone, researchers consider the arrangement of the jaw and cartilage together. Understanding where the teeth sat inside the mouth is necessary for studying its feeding habits.^[1]

Fossil discovery

UMUT PV07477 at the University of Tokyo museum is tooth-row material of this species from Japan. Other research compared the proportions of multiple tooth rows to reassess species distinctions. A museum collection item and comparisons among specimens worldwide together help reveal the animal’s form.^[3][2]

References

1. Tapanila et al.2020 — Saws, scissors and shark teeth
2. Unraveling species concepts for the Helicoprion tooth whorl
3. University Museum, University of Tokyo — Helicoprion bessonowi
4. Lane·Maisey (2009) — Pectoral-fin structure of Tribodus

Research questions

Where in the body did the whorl sit? Researchers study the mouth by comparing several tooth rows and jaw materials together. Connecting unusual teeth with the structure of the whole mouth shows how fossil interpretations change.^[1][2]

Observation

Follow the teeth along the inside and outside of the whorl. Imagining their row within the lower jaw reveals an animal’s body beyond a simple circular fossil.^[1]