| Edestus Temporal range: Late Carboniferous | |
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| An artist's illustration of Edestus | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Holocephali |
| Order: | †Eugeneodontida |
| Family: | †Edestidae |
| Genus: | †Edestus Leidy, 1856 |
| Referred species | |
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Edestus is a eugeneodontid holocephalian shark-like fish that lived during the late Carboniferous. Fossils have been found in Russia, the UK and the USA. Despite resembling a shark, it is (like all eugeneodonts) closer to extant chimaeras.
Description[]
Reconstruction
The whorls of Edestus are composed of numerous serrated teeth that have long v-shaped roots that are stacked on top of each other akin to roof tiling. Up to a dozen teeth are present in each whorl at any one time. Teeth grew in the back end (posterior) of the whorl, and gradually migrated forward through the whorl, before being ejected at the front end (anterior). Up to 40 teeth could have grown in each whorl during the lifetime of the animal. The upper and lower whorls are distinct in their morphology, with the lower whorl having a greater degree of curvature.
As with most cartilaginous fish, preserved skeletal material is rare, due to the cartilage of the skeleton having a poor potential for fossilisation. Several specimens with the preserved cranial remains of Edestus have been reported, the most important being FMNH PF2204, a crushed juvenile specimen, likely representative of E. heinrichi, which preserves both upper and lower blades in association with a well preserved chondrocranium and jaws. The Meckel's cartilage of the lower jaw is approximately 1.5 times the length of the lower whorl, the end of the lower whorl extends forward beyond the edge of the Meckel's cartiilage. The Meckel's cartilage was articulated with a slender quadrate via a socket in the Meckel's cartilage which articulated with a process of the quadrate. The quadrate at its other end articulated with the otic process of the chondrocranium, the structure that houses the brain and sensory organs. The upper tooth blade was rigidly held between two plates of palatine cartilage, which at their front ends are crescent shaped, matching the curvature of the tooth whorl, with the upper whorl extending forward beyond the cartilage. The chondrocranium was capped by a shield-shaped dorsal plate.
No postcranial remains are known of Edestus. However, the body shape can be estimated via postcranial remains known from a few eugeneodonts. Eugeneodonts with preserved postcrania include the Pennsylvanian to Triassic-age caseodontoids Caseodus, Fadenia, and Romerodus.
These taxa have a fusiform (streamlined, torpedo-shaped) body plan, with triangular pectoral fins. There is a single large and triangular dorsal fin without a fin spine, and a tall, forked caudal fin which externally appears to be homocercal (with two equally-sized lobes). This general body plan is shared by active, open-water predatory fish such as tuna, swordfish, and lamnid sharks. Eugeneodonts also lack pelvic and anal fins, and judging by Romerodus, they would have had broad keels along the side of the body up to the caudal fin. Fadenia had five well-exposed gill slits, possibly with a vestigial sixth gill. There is no evidence of the specialized gill basket and fleshy operculum present in living chimaeroids.
The cranium of FMNH PF2204 is around 25 centimetres in length, and the associated upper and lower whorls have lengths of 10.4 and 8 cm respectively. The largest known individuals of E. heinrichi are an upper whorl 32 cm in length and a lower whorl 43 cm in length. The estimated minimum length of the skulls of these individuals based on allometry are around 77 cm and 134 cm respectively. Based on a 5:1 body length to head ratio, this suggests that individuals of E. heinrichi could reach lengths of 6.7 m.
Paleobiology[]
Due to the unusual nature of the tooth whorls and the historic lack of cranial material, many hypotheses for how the whorls functioned have been proposed. Early hypotheses suggested that they were indeed teeth or were defensive spines located on the fins. Wayne M. Itano proposed that the whorls were arranged vertically to slash prey. In the description of the cranial material of Edestus, Tapanila and colleagues (2018) found that the tooth whorls functioned as effective grasping and slicing tools for soft bodied prey. The jaws of Edestus were operated by a two gear system, involving double jointing of the quadrate bone allowing for forward and backward movement of the lower jaw, similar to the streptostyly seen in living squamates, with an estimated force ouput of 1907 newtons. The authors proposed that during prey approach, adductor muscles pulled the Meckel's cartilage of the lower jaw upwards and forwards to close the jaw, causing each tooth to slice roughly three times its length, and further push the prey into the teeth of the upper whorl. During the subsequent opening of the jaw mouth the Meckel's cartilage moved backwards and downwards by the adductor muscles, causing further slicing.
In Popular Culture[]
- Edestus can also be created in the Aquatic Park of Jurassic Park: Builder. It was at first only purchasable in real-world money. Since April 30th 2016, it became a DNA tournament limited edition.
- Edestus is a tournament surface creature in Jurassic World: The Game.