Ostenoselache

***Ostenoselache*** (literally meaning "shark from Osteno") is an extinct genus of shark of obscure familial relationships that lived during the early Jurassic Period in what is now Osteno, in Italy. It had an unusually long rostrum and may have been the only known shark to house electrical discharge organs for defensive and hunting purposes.

## Description

This very small shark possessed a unique body form that was very different from that of any other extinct or living sharks. The body was very slender, and in total the animal could reach a maximum length of about 30 cm (11 in). The spine was formed from about 150 vertebrae.

The skull, poorly preserved in most specimens, was very peculiar: the orbits were large, indicating it had large eyes, while the jaw was long and thin and fitted with about 30 simple, singly-cusped teeth. The skull protruded into an elongated and flattened rostrum, projecting far beyond the mouth; The rostrum was completely different from the structure present in animals such as sawfish, goblin sharks or rays such as guitarfish, and was composed of a complex cartilaginous skeleton with a series of forward-projecting branches.

The fins are not well known in Ostenoselache, but many specimens retain the additional cartilage that forms the male's pelvic appendix. The anus was well positioned forward, and the tail was very long. *Ostenoselache* is the only shark possessing only one median fin, the anal fin, extended from the anus to the tip of the tail and supported by numerous radial cartilage ridges.

## Classification

Although this animal is known for its well-preserved fifty specimens from Osteno (Italy), the classification of *Ostenoselache* is unclear because of its highly peculiar morphology. As such, it is generally uncertain as to what family of sharks this species belongs. However, the scholar preferred to classify it in a family of its own, **Ostenoselachidae**, well distinguished from the contemporary group known as paleospinacid sharks that lived at the same time.

Ostenoselac is not the only electrical cartilaginous fish: modern torpedo rays, for example, possess a rather powerful electric apparatus, but only appeared in Miocene (185 million years later than *Ostenoselache*). *Ostenoselache* is therefore the oldest known electrical cartilaginous fish, and also the only one to have developed a serpentine body shape. Additionally, it is the only shark known to have possessed possible electrical abilities.

## Possible Electrical Abilities

According to paleontologist Christopher Duffin, who studied *Ostenoselache* in 1998, the only fish vaguely similar to this animal are the current representatives of the knife fish family, which also include the electric eel (*Electrophorus electricus)*. Like the latter, *Ostenoselache* also had a long tail and the only fin the tail supported was a very long anal fin that merged with its caudal fin; The modern electric eel has electrical organs (modified muscles that generate an electrical field) that can occupy upwards of 80% of the length of its body, and sense organs that can interpret the distortions of this field. According to Duffin, *Ostenoselache* also likely possessed similar organs along the body; The strange structure on the head, on the other hand, is thought to have been used for electroreception, like in most known sharks.

## Paleobiology

The forward movement of the intestines and other organs of *Ostenoselache* and the remarkable expansion of the tail suggests that the shark's caudal muscles could be modified to form electrical organs, through which *Ostenoselache* produced fields for orientation in the dark waters of the sea where it lived, which were likely turbid and murky due to algal decay.

*Ostenoselache* was supposedly able to detect the electric fields due to the elongated skeleton structure and it is assumed because of this that that it could generate electric shocks for attack and defense. Its modern analogue, the electric eel, is capable of producing 600 volts, both for predatory behavior and defending itself. In any case, the small size of *Ostenoselache* did not make it so efficient as to be invulnerable: many of its fossil remains were found inside other fossils such as those of a large thylacocephalian arthropod, *Ostenocaris*, which seems to have preyed on *Ostenoselache*.