Heliocoprion
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Helicoprion Temporal range: Cisuralian-Guadalupian |
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| Tooth-whorl, Utah Field House of Natural History | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Order: | †Eugeneodontida |
| Family: | †Helicoprionidae |
| Genus: |
†Helicoprion Karpinsky, 1899 |
| Type species | |
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Helicoprion bessonowi Karpinsky, 1899 |
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| Species | |
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Helicoprion is a long-lived genus of extinct, shark-likeeugeneodontid holocephalid fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called "tooth whorls"— the cartilaginous skull, spine, and other structural elements have not been preserved in the fossil record, leaving scientists to make educated guesses as to its anatomy and behavior. Helicoprion lived in the oceans of the early Permian290 million years ago, with species known from North America, Eastern Europe, Asia, and Australia. The closest living relatives of Helicoprion (and other eugeneodontids) are the chimaeras.
In 2011, a tooth whorl from a Helicoprion was discovered in the Phosphoria site in Idaho. The tooth whorl measured 45 cm (18 in) in length. Comparisons with other Helicoprion specimens show that the animal that sported this whorl would have been 10 m (33 ft) in length, and another, even bigger tooth whorl that was discovered in 1980s (but was not published until 2013) which the discoverers dubbed IMNH 49382 or "Boise" was discovered at the same site. The whorl is incomplete, but in life it would have 60 cm (24 in) long and would have belonged to an animal that possibly exceeded 12 m (39 ft) in length, making Helicoprion the largest known eugeneodont.
Until 2013, the only known fossils of this genus on record were their teeth, which were arranged in a "tooth-whorl" strongly reminiscent of a circular saw. As the skeletons of chondrichthyid fish are made of cartilage, including those of Helicoprion and other eugeneodonts, the entire body disintegrates once it begins to decay, unless exceptional circumstances preserve it. The tooth-whorl was not realized to be in the lower jaw until the discovery of the skull of a related genus of eugeneodont, Ornithoprion. The tooth-whorl represented all the teeth produced by that individual in the lower jaw; as the individual grew, the older, smaller teeth were moved into the center of the whorl by larger, newer teeth appearing. Models of the Helicoprion tooth-whorl have been made. In the 1994 book Planet Ocean: A Story of Life, the Sea, and Dancing to the Fossil Record, author Brad Matsen and artist Ray Troll describe and depict an example of such a model. They proposed that no teeth were present in the animal's top jaw besides the crushing teeth for the whorl to cut against. The two envision the living animal to have a long and very narrow skull, creating a long nose akin to the modern-day goblin shark. According to their studies, the fossils that have been found are essentially a growth ring, as each set of new teeth pushes the previous set into the whorl.
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Wikipedia