Helicoprion facts for kids
Quick facts for kids Helicoprion |
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| Tooth-whorl, Utah Field House of Natural History | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Order: | †Eugeneodontida |
| Family: | †Helicoprionidae |
| Genus: | †Helicoprion Karpinsky, 1899 |
| Type species | |
| Helicoprion bessonowi Karpinsky, 1899
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| Species | |
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Helicoprion is a genus of extinct, shark-like eugeneodontid holocephalian fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called "tooth whorls", which in life were embedded in the lower jaw. As with most extinct cartilaginous fish, the skeleton is mostly unknown. Helicoprion lived in the oceans of the Early Permian (Cisuralian) 290 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. The unusual tooth arrangement is thought to have been an adaption for feeding on soft bodied prey, and may have functioned as a deshelling mechanism for hard bodied cephalopods such as nautiloids and ammonoids.
Contents
History of Discovery
The first specimen of Helicoprion to be described was a small tooth whorl (WAMAG 9080) found in Western Australia, named in 1886 by Henry Woodward as Edestus davisii. Helicoprion was first named by Alexander Karpinsky in 1899 from 6 specimens found in Artinskian-age limestones of the Ural Mountains, assigned to the newly designated type species Helicoprion bessonowi. The publication also transferred Edestus davisii to Helicoprion. In studies in 1907 and 1909, Oliver Perry Hay described the new genus and species Lissoprion ferrieri for fossils found in phosphate deposits on the border between Idaho and Wyoming. This species was transferred to Helicoprion by Karpinsky in 1911. In a publication from 1939 Harry E. Wheeler described two new species of Helicoprion. Helicoprion sierrensis was described from a specimen (UNMMPC 1002) found in glacial moraine deposits in Eastern California, likely originating from the Goodhue Formation. Helicoprion nevadensis was described from a now lost specimen (UNMMPC 1001) found in a mine in Nevada, with uncertain geological provenance. Helicoprion mexicanus was described in 1945 by Müllerreid. Svend Erik Bendix-Almgreen published a monograph in 1966 on specimens of Helicoprion in Idaho museums and named a new species, Helicoprion ergassaminon. In 1970 a specimen (PMO A-33961) found in Svalbard, Norway was described by Siedlecki as the new species Helicoprion svalis. In 2007 Helicoprion jingmenense, was described by Chen and colleagues from a large and complete tooth whorl (YIGM V 25147) discovered during road construction in Hubei, China. In 2013, systematic revision of Helicoprion via morphometric analysis of the tooth whorls found only H. davisii, H. bessonowi and H. ergassaminon to be valid, with some of the larger tooth whorls being outliers. Helicoprion specimens are known from the Early Permian (Cisuralian). Fossils have been found in the Ural Mountains, Western Australia, China, and Western North America, including the Canadian Arctic, Mexico, Idaho, Nevada, Wyoming, Texas, Utah, and California. More than 50% of Helicoprion specimens are known from Idaho, with an additional 25% being found in the Ural Mountains.
Historical reconstructions
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 upper 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.
For over a century, whether the tooth-whorl was situated in the lower jaw was not certain. Older reconstructions placed the whorl in the front of the lower jaw. A 2008 reconstruction, created by Mary Parrish under the direction of Robert Purdy, Victor Springer, and Matt Carrano for the Smithsonian, places the whorl deeper into the throat, although other studies did not accept this conclusion.
Description
Tooth whorls
Almost all Helicoprion specimens are known solely from "tooth whorls", which consist of dozens of teeth embedded within a logarithmic spiral-shaped root composed of osteodentine, beneath which lies a shaft of calcified cartilage. The earliest juvenile tooth within the spiral is hooked, but adult teeth are generally triangular in shape, laterally compressed and often serrated, which point forward in the spiral. The tooth whorls essentially serve as a growth ring, as each set of new teeth pushes the previous set into the whorl.
Cartilaginous skull
As the skeletons of chondrichthyan 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. There is one known Helicoprion specimen which is preserved to such an extent that portions of the cartilaginous skull can be studied. This specimen, IMNH 37899, was found in Idaho in 1950 and redescribed in 2013. CT scanning showed that alongside the tooth whorl, the specimen uniquely preserves in 3 dimensions the cartilage of the upper and lower jaw. The upper jaw consists of a palatoquadrate, which in life articulated with the neurocranium. There is no evidence of an articulation with the hyomandibula, and teeth appear to be absent from the upper jaw. The Meckel's cartilage of the lower jaw has an upward process that abuts a downward projection of the palatoquadrate, which may have served to stop the tooth whorl from puncturing the upper jaw. The studies reconstruction places the tooth-whorl at the back of the jaw, where the tooth-whorl occupied the entire mandibular arch.
Valid species
H. bessonowi
The type species of Helicoprion, Helicoprion bessonowi, was first described by Alexander Karpinsky in 1899 alongside the genus itself. This species can be differentiated from others by a short and narrowly spaced tooth whorl, backward-directed tooth tips, obtusely-angled tooth bases, and a consistently narrow whorl shaft. One of two Helicoprion species described by Wheeler in 1939, H. nevadensis, is based on a single partial fossil found in 1929 by Elbert A Stuart. It was reported as having originated from the Rochester Trachyte deposits, which Wheeler considered to be of Artinskian age. However, the Rochester Trachyte is in fact Triassic, and H. nevadensis likely did not originate in the Rochester Trachyte, thus rendering its true age unknown. Wheeler differentiated H. nevadensis from H. bessonowi by its pattern of whorl expansion and tooth height, but Leif Tapanila and Jesse Pruitt showed in 2013 that these were consistent with H. bessonowi at the developmental stage that the specimen represents.
Based on isolated teeth and partial whorls found on the island of Spitsbergen, Norway, H. svalis was described by Stanisław Siedlecki in 1970. The type specimen, a very large whorl, was noted for its narrow teeth that apparently are not in contact with each other, but this seems to be a consequence of only the central part of the teeth being preserved, according to Tapanila and Pruitt. Since the whorl shaft is partially obscured, H. svalis cannot be definitely assigned to H. bessonowi, but it closely approaches the latter species in many aspects of its proportions. With a maximum volution height of 72 mm (2.8 in), H. svalis is similar in size to the largest H. bessonowi, which has a maximum volution height of 76 mm (3.0 in).
H. davisii
H. davisii was described initially from a series of 15 teeth found in Western Australia. They were described by H. Woodward in 1886 as a species of Edestus, E. davisii. Upon naming H. bessonowi, Karpinsky also reassigned this species to Helicoprion, an identification subsequently supported by the discovery of two additional and more complete tooth whorls in Western Australia. The species is characterized by a tall and widely spaced tooth whorl, with these becoming more pronounced with age. The teeth also noticeably curve forwards. During the Kungurian and Roadian, this species was very common worldwide.
H. ferrieri was originally described as a species of the genus Lissoprion in 1907, from fossils found in the Phosphoria Formation of Idaho. An additional specimen, tentatively referred to H. ferrieri, was described in 1955. That specimen was found in Wolfcampian-age quartzites exposed on China Mountain, six miles southeast of Contact, Nevada. The 100-mm-wide fossil consists of one and three-quarters whorls and about 61 preserved teeth. Due to weathering, the rest of the fossil was lost and the preserved section is distorted from slippage of the host rock. While initially differentiated using the metrics of tooth angle and height, Tapanila and Pruitt considered these characteristics to be intraspecifically variable, reassigning H. ferrieri to H. davisii.
H. jingmenense was described in 2007 from a nearly complete tooth whorl with four and a third volutions (part and counterpart) found in the Lower Permian Qixia Formation of Hubei Province, China. It was discovered during road construction. The specimen is very similar to H. ferrieri and H. bessonowi, though it differs from the former by having teeth with a wider cutting blade, and a shorter compound root, and differs from the latter by having fewer than 39 teeth per volution. Tapanila and Pruitt argued that the specimen was partially obscured by the surrounding matrix, resulting in an underestimation of tooth height. Taking into account intraspecific variation, they synonymized it with H. davisii.
H. ergassaminon
H. ergassaminon, the rarer species from the Phosphoria Formation, was described in detail within a 1966 monograph by Svend Erik Bendix-Almgreen. The holotype specimen ("Idaho 5"), now lost, bore breakage and wear marks indicative of its usage in feeding. Several referred specimens exist, none of which show wear marks. This species is roughly intermediate between the two contrasting forms represented by H. bessonowi and H. davisii, having tall but narrowly-spaced teeth. Its teeth are also gently curved, with obtusely-angled tooth bases.
Other material
Several large whorls are difficult to assign to any particular species group, H. svalis among them. IMNH 14095, a specimen from Idaho, appears to be similar to H. bessonowi, but it has unique flange-like edges on the apices of its teeth. IMNH 49382, also from Idaho, has the largest known whorl diameter at 56 mm (2.2 in) for the outermost volution (the only one preserved), but it is incompletely preserved and still partially buried.
H. mexicanus, named by F.K.G. Müllerreid in 1945 and supposedly distinguished by its tooth ornamentation, has a holotype that is currently missing, but its morphology was similar to IMNH 49382. In the absence of other material, it is currently a nomen dubium. Vladimir Obruchev described H. karpinskii from two teeth in 1953. He provided no distinguishing traits for this species, thus it must be regarded as a nomen nudum.
Images for kids
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Restoration of the skull of Helicoprion, based on IMNH 37899
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IMNH 30900, a Helicoprion ergassaminon tooth-whorl from Gay Mine in Bingham County, Idaho.
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See also
In Spanish: Helicoprion para niños
