Edestus is an extinct genus of eugeneodontid holocephalian fish known from the Late Carboniferous (Pennsylvanian) of the United Kingdom, Russia, and the United States. Most remains consist of isolated curved blades or "whorls" that are studded with teeth, that in life were situated within the jaws. Edestus is a Greek name derived from the word edeste (to devour), in reference to the aberrant quality and size of the species' teeth. The largest species, E. heinrichi, has been conservatively estimated to reach greater than 6.7 m (22 ft) in length, around the size of the largest known great white shark.
Like its other relatives, such as Helicoprion, and unlike modern sharks, the species of Edestus grew teeth in curved blades or "whorls". In Edestus' case, only a single row of teeth occurred in the midline of each jaw, leading Edestus to sometimes be described as the "scissor tooth shark". The degree of curvature in the teeth brackets, along with size, are distinct in each species.
History of discovery
Edestus was first described by Joseph Leidy in 1856. The type species is Edestus vorax, the holotype specimen (ANSP 9899) is very fragmentary and of uncertain stratigraphic and geographic provenance, reported to be from Muskogee County, Oklahoma, though this has been questioned. In 1855 Edward Hitchcock presented a specimen of Edestus to the American Association for the Advancement of Science meeting at Providence, Rhode Island the specimen (a tooth whorl) had been originally found in Parke County, Indiana. The specimen was loaned to famed British anatomist Richard Owen in 1861, who referred the specimen to Edestus and suggested that it was a fin spine. Edestus minor was described in 1866 by John Strong Newberry based on AMNH FF477, a single crown that lacks most of the root from Posey County, Indiana. Edestus heinrichi was described in 1870 by Newberry and Amos Henry Worthen from a now-lost specimen found in Illinois. Edestus triserratus was described in 1904 by Edwin Tulley Newton, from GSM 31410, which was found in the Coal Measures in Staffordshire, England which is a partial tooth lacking the apex of the crown. Oliver Perry Hay in 1912 was the first to describe an associated pair of upper and lower tooth whorls (USNM V7255), found in a coal mine near Lehigh, Iowa, which he assigned to the new species Edestus mirus, now thought to be a synonym of Edestus minor. Specimens of Edestus are also known from the Moscow Basin on the Russian Platform. Edestus karpinskii was described by A.B. Missuna in 1908 from remains found near Kolomna around 100 km southeast of Moscow. Edestus minusculus was described by Hay in 1912 from a specimen originally described by Alexander Karpinsky as Edestus cf. minor from a specimen found at the Myachkova quarry, near Moscow.
Description
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 articlulated 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.