Helicoprion

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Helicoprion
Helicoprion tooth spiral

Helicoprion tooth spiral

Temporal occurrence
Artinskium to Roadium ( Perm )
279.5 to 268.8 million years
Locations
  • Russia
  • North America (Canada, USA, Mexico)
  • Japan
  • Australia
Systematics
Superclass : Jaw mouths (Gnathostomata)
Class : Cartilaginous fish (Chondrichthyes)
Subclass : Holocephali
Order : Eugeneodontiformes
Family : Agassizodontidae
Genre : Helicoprion
Scientific name
Helicoprion
Karpinsky , 1899

Helicoprion is an extinct genus of cartilaginous fish from the lower and middle Permian around 250 million years ago that belonged to the Euchondrocephali . Their closest relatives today are the sea ​​cats .

features

Helicoprion , speculative life reconstruction

The fossil- preserved tooth spirals are characteristic of the Helicoprion genus . In each fish, these consisted of a single spiral-shaped row of narrow teeth, which in adult animals had more than three circumferences of up to 180 teeth.

The exact location of the spiral on the animal was unclear for a long time. In the meantime, however, we know from computed tomographic examinations on the fossil IMNH 3789 of the Idaho Museum of Natural History that it was suspended on the labial cartilage and embedded median between the two Meckel's cartilages , so that the center of the tooth spiral lay median between the upper and lower jaw, the diameter of the Tooth spiral corresponded roughly to the length of the lower jaw.

As usual with cartilaginous fish, the upper jaw consisted of the two median fused palato- square cartilages and the lower jaw of the right and left Meckel's cartilage and the right and left labial cartilage . The tooth spiral in the specimen IMNH 3789 had a diameter of 23 cm and contained 117 teeth.

Helicoprion has an autodiastyle jaw suspension , as is usual for Euchondrocephali . That means: The upper jaw ( palatoquadratum ) is two-hinged (right and left ) attached to the skull ( neurocranium ). And the lower jaw is in turn hooked into the upper jaw with two hinges. ( Cave : the autodiastyle jaw suspension is not to be confused with the autostyle jaw suspension.)

function

It is believed that the helical row of teeth took on the function of an oscillating (back and forth rotating) circular saw that sawed and ground cuttlefish such as nautilids and ammonites .

Earlier reconstructions

For a long time there was a lack of clarity about the function and position of the tooth spiral. Mostly they were arranged at the tip of the lower jaw, less often at the upper jaw tip, on the dorsal fin, analogous to the toothed, anvil-shaped dorsal fin of male Stethacanthus or on the caudal fin. It has been speculated that it was a case of Peckham's mimicry and that the spiral was intended to attract ammonites that were subsequently eaten, or that it was a special bite for biting clams. It could also have served to make schooling fish immobile or kill them by violently beating them back and forth, similar to how the recent saw rays (Pristiformes) use their saws.

Systematics

Systematically, Helicoprion belongs to the Eugeneodontiformes , a group of cartilaginous fish with similar dentition, a group possibly distantly related to the recent sea ​​cats (Chimaeriformes), which, in contrast to them, had shark-like teeth that were constantly being replaced.

literature

Individual evidence

  1. ↑ a b c L. Tapanila, J. Pruitt, A. Pradel, CD Wilga, JB Ramsay, R. Schlader, DA Didier: Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion . In: Biology Letters . tape 9 , no. 2 , February 6, 2013, article 20130057 , doi : 10.1098 / rsbl.2013.0057 (English, royalsocietypublishing.org [PDF; accessed April 13, 2014]).
  2. ↑ Girish Chandra: Jaw Suspension in Vertebrates. Iaszoology, accessed April 13, 2014 .

Web links

Commons : Helicoprion  - collection of images, videos and audio files