Helicoprion

Introduction

Helicoprion is an extinct genus of shark-like eugeneodont fish (a group of extinct cartilaginous fishes). Members of Eugenodontida possess a unique morphological feature called “tooth whorls”. They first appeared in the Devonian before going extinct in the Early Triassic.

3D interactive model of Helicoprion

_{3D model made by cdmstudio.com.au}

Identification

Helicoprion, like other chondrichthyan fish, had skeletons made of cartilage. Unfortunately, this makes it difficult to determine what Helicoprion looked like because the skeleton didn’t fossilise easily. Almost all Helicoprion specimens are fossilised 'tooth whorls' that consist of teeth embedded in a spiraled root.

In the 1900s, scientists debated where these tooth whorls were located on the animal. Some postulated that the spiral sat on the lower jaw, some claimed it sat on the upper jaw, and yet others claimed it sat on the dorsal fin. However, the recent description of fossils that preserve cartilage around the teeth confirm that the spiral teeth sit in the lower jaw (Tapanila et al. 2013).

Habitat

Fossils of Helicoprion have been found across America, Australia, Asia and Europe, indicating that it had a global distribution during the Permian.

Feeding and diet

Understanding the unique teeth and lower jaw of Helicoprion was important for scientists as it was the key to understanding the ecology and evolution of this peculiar shark. Scientists first argued that hard-shelled prey items, such as ammonoids, would slip out of the mouth due to the shape of the tooth whorl. However, reconstructions indicate that soft prey items, such as squids, would be trapped in the tooth whorl, making them difficult to ingest (Ramsay et al. 2015).

It wasn’t until the application of biomechanical principles that scientists were able to reveal how this predator consumed its prey. Amazingly, each tooth had a different function depending on its position in the tooth-whorl: anterior teeth hooked and dragged prey into its mouth, the middle teeth pierced and cut the prey, whilst the posterior teeth cut and pushed the prey into its oral cavity (Ramsay et al. 2015). This unique feeding apparatus would have allowed Helicoprion to consume both hard- and soft bodied prey items using different feeding strategies (Ramsay et al. 2015).