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Not to be confused with Parahelicampodus or Paredestus.
Gasmasque/sandbox2
Temporal range: Early Permian (Asselian-Artinskian),
~298.9-283.5 Ma
The type specimen of Parahelicoprion clerci in lateral (1a) and transverse (1b) views
Additional segments of the P. clerci holotype which were broken during collection
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Holocephali
Order: †Eugeneodontida
Family: †Helicoprionidae
Genus: †Parahelicoprion
Karpinsky, 1924
Type species
Helicoprion clerci
Karpinsky, 1916
Species
  • P. clerci Karpinsky, 1916
  • P. mariosuarezi Merino-Rodo & Janvier, 1986
Synonyms
  • Helicoprion? (Karpinsky, 1899)
  • Physonemus grandis? (Moore)

Parahelicoprion (meaning "near spiral saw" or "near Helicoprion") is an extinct genus of shark-like cartilaginous fish known from the early Permian Artinskian Beds of the Ural Mountains of Russia and the Copacabana Formation of Bolivia. Members of the genus possessed a row of large tooth crowns on the midline of the lower jaw, known as a tooth whorl. The characteristics of this whorl are unique to fishes of the order Eugeneodontida, and more specifically the family Helicoprionidae, to which Parahelicoprion belongs. The genus name refers to Helicoprion ('spiral saw'), another eugeneodont from the Ural Mountains which bore a similar midline tooth arrangement. Two species of Parahelicoprion are assigned; the Russian P. clerci and the Bolivian P. mariosuarezi.

The holotype of Parahelicoprion clerci, which consists only of tooth fragments, was badly damaged by mining. That of the Bolivian P. mariosuarezi consists of only nine partial teeth; all of which are missing their outer edges. Estimates of the extent of the complete whorl, body size, and ecology of Parahelicoprion are highly speculative as a result of its incomplete fossils, although it is assumed to have been very large, predatory, and pelagic. When first described, P. clerci was considered a species of Helicoprion, although its initial describer, Alexander Karpinsky, later separated it into its own genus. It has since been suggested that this genus may indeed represent a junior synonym of Helicoprion or a paraphyletic, non-diagnostic taxon.

Discovery and naming

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Photograph of Alexander Karpinsky, who named and described Parahelicoprion clerci

The type specimen of Parahelicoprion was initially named Helicoprion clerci by influential Russian geologist Alexander Karpinsky. This specimen was found by a miner in the Ural Mountains region of Russia,[1][2] in strata dated to the Artinskian stage of the Cisuralian epoch (early Permian).[3][4] The rocks which produced P. clerci has subsequently been defined as part of the Divjinskian Formation (alternatively spelled Divya Formation)[3][5] and are composed of marlstone.[1] Karpinsky reassigned this specimen to its own genus in 1924,[6] although he had already informally referred to it as Parahelicoprion in a publication two years prior and had even suggested it warranted its own genus in the initial 1916 description.[7][1] The name, P. clerci, honors Onisim Egorovič Clerc, who at the time of its description was the president of the Ural Naturalist's Society. The exposure of the Divya Formation where the type specimen was found is near the town of Krasnoufimsk,[1][2] and a cast of this material was subsequently housed at the Krasnoufimsk Museum.[8]

Location of Krasnoufimsk (red), where the remains of Parahelicoprion clerci originate

A second species, Parahelicoprion mariosuarezi, was described and tentatively assigned to the genus in 1986 by Dagmar Merino-Roda and Phillipe Janvier. This species, which is based on a single large specimen (designated no. 6097, YPFB), was discovered in the Copacabana Formation of Yauri chambi, Bolivia, and was dated to the Asselian stage of the early Permian.[9][10] The holotype, a three-dimensional partial tooth whorl,[10] was found preserved in a layer of calcarious red sandstone. The species is named in honor of Dr. Mario Suarez-Riglos,[9] and the type specimen is currently housed in the collection of the Noel Kempff Mercado Natural History Museum.[11]

The genus derives its name from the Greek prefix -para, meaning "near" or "beside" and from the name of the related Helicoprion,[12] itself meaning "coiled saw'" or "spiral saw".[13][14][15] In scientific nomenclature, -para is often used to denote similarity or relation.[16][17]

Description

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Speculative life reconstruction of Parahelicoprion clerci, which conforms to that of P. mariosuarezi featured in Phillipe Janvier's Early Vertebrates (1996)

Both Parahelicoprion species are extremely incompletely known,[18] and the only material which has been assigned confidently to the genus consist of fragments of the lower symphyseal (midline) tooth whorl, significantly limiting available information.[19][8] While some authors have suggested the genus lacks defining, autapomorphous features,[9] the tooth crowns of both species of Parahelicoprion are noted to share extremely long, backwards-sweeping lower sections (referred to as "wings" or "ribs") which extend nearly to the base of the tooth root, as well as curved denticles or serrations along the edges of the crowns.[4] In addition to tooth whorls, it has been suggested that large, forward-arching fin spines under the ichthyodorulite form-genus Physonemus may have belonged to Parahelicoprion and related eugeneodonts,[3][20] with the specific species P. grandis suggested to correspond to Parahelicoprion clerci.[20][21] In a 2023 publication, researcher Serge Naugholnykh has asserted personal belief that these spines correspond to edestoids,[3] although sickle-like ichthyodorulites are believed by most modern researchers to represent the copulatory organs of symmoriiform fishes.[4][22][23] Members of the Eugeneodontida are today generally assumed to have lacked fin spines.[4][15][24]

The postcranial anatomy of eugeneodonts has been suggested to vary little between genera,[24] indicating that, like their smaller relatives, both species of Parahelicoprion possessed long, fusiform bodies with crescent-shaped caudal fins, and that they lacked pelvic and anal fins.[9][24] In his 1996 textbook Early Vertebrates, researcher Philippe Janvier reconstructs P. mariosuarezi (which he contributed to describing) with a proportionally very small, short tooth whorl situated at the tip of a pointed, greatly elongated pair of jaws.[25] This anatomy is also suggested in the animal's initial description, and is assumed based on the partial skull of Sarcoprion edax and the well-preserved fossils of the related caseodontoids.[9][24] In his 1916 description of Parahelicoprion clerci (then Helicoprion clerci), Karpinsky assumes the whorl of the species formed a large spiral,[1] and some subsequent authors have agreed that the shape of the whorl in life would have been indistinguishable from that of Helicoprion.[3][26]

Parahelicoprion clerci

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Reconstructed teeth of P. clerci in lateral (1a) and transverse (1b, 2b) views, compared with the teeth of Helicoprion (3, 4)[1]

The type specimen of Parahelicoprion clerci consists of five badly damaged tooth fragments, all found in association and believed to belong to a single tooth whorl. Three of these fragments were subsequently glued together during preparation in order to reflect their in-life articulation.[1] Later sources have reported a holotype specimen spanning 25 cm (10 in) across and consisting of six tooth crowns,[9][13][24] based on a reconstructed cast of the material photographed by ichthyologist Svend Erik Bendix-Almgreen during the 1970s.[8] Alexander Karpinsky believed that the material he described represented only a small portion of the tooth whorl as it was preserved, with the rest having been either destroyed or not collected during mining. The surface texture and enameloid of the specimen is also noted to have been severely degraded. No lateral dentition is confidently known in this species,[7] although crushing teeth similar to those of Campodus may have been present.[21][27] The general shape of the reconstructed whorl fragments observed in Parahelicoprion clerci has been compared to that of the potential close relative Sarcoprion by various authors,[4][8][24] although Svend Erik Bendix-Almgreen insists that the material of the former is too poorly known for such comparisons to be confidently made.[8]

Tip of the tooth crown's "wing" or "rib" in P. clerci, displaying this species' unique arrangement of serrations (above) and crenulations (below)[4]

The largest tooth crown tip (not including the serrated "rib") of the holotype is measured by Karpinsky at 3.4 cm (1.3 in) in height, 3 cm (1.2 in) across, and 1.9 cm (0.7 in) wide at the widest point, while the smaller known tip measures 2.4 (1.0 in) cm in height, 2.9 cm (1.1 in) across and 1.5 cm (0.6 in) in height. This dramatic shift in size across a small portion of the whorl is noted to be different than that observed in Helicoprion bessonowi, in addition to the fact that the largest P. clerci tooth crown is significantly larger than that of the former.[1] The posterior edges of the crown tips thin to form sharp cutting blades.[1][7] The uppermost tips of the tooth crowns are noted to be uniquely rounded and blunt, rather than coming to a point as in many other edestoids.[1] As in other members of its family, the teeth of the whorl angle forward in the mouth.[24] The "ribs" or "wings" (long segments which anchor to the root), which curve gently towards the back of the jaws, are extremely elongated and are lined with very deep, downward-angled serrations along the anterior edge and crenulations along the sloping posterior edge.[1][4][24] The form of these serrations and crenulations is characteristic of this species.[1]

The teeth are described by Karpinsky as being coated in enamel,[1] although this substance has subsequently been identified as enameloid or vitrodentine as in other helicoprionids.[24][28] The interior of the teeth was composed of a spongy form of dentin, identified in the taxon's description as vasodentin (a form common amongst fishes).[1][7]

Parahelicoprion mariosuarezi

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The holotype whorl of Parahelicoprion mariosuarezi is described as larger than that of P. clerci.[9][13] Merino-Rodo and Janvier (1986) state that it is likely nearly complete, with the exception of the cutting edges along the upper part of the whorl being broken off.[9] Unlike the type species, serrations and crenulations are absent along most of the crown, but several large, pointed denticles do protrude along the lingual (lower) edges of the third to ninth tooth crowns. This species also preserves a single denticle-bearing parasymphyseal tooth along the edge of the whorl, a tooth type which is not known from P. clerci. The holotype of P. mariosuarezi shows the smallest crown was positioned anteriorly at the very front of the preserved portion of the whorl and was significantly smaller than the next crown in the sequence,[4][9] which is suggested to indicate that the whorl was short and did not form a helical spiral. If the type of P. mariosuarezi is nearly complete as suggested in its description, then the whorl, which as preserved possesses nine tooth crowns,[9] bore far fewer crowns than related genera such as Helicoprion, which may have had between 130-180.[14][29][30] Despite being unpreserved, the outer cutting edges of the teeth in P. mariosuarezi are thought to have conformed in shape and orientation to those of the type species, due to the preserved portions of the crowns being similar in shape and thickness. The root of the rear section of the whorl is entirely fused.[9]

Classification

[edit]
Whorl segments of P. clerci illustrated in lateral (3) and transverse (4) views, compared with those of the related eugeneodonts Campodus, Helicoprion, and Edestus[7]

When first named by Karpinsky, Parahelicoprion was considered a member of the family Edestidae, which at that time also encompassed genera such as Helicoprion and Campodus.[7] While the relation and classification of edestids and helicoprionids was variable throughout the 20th century,[24][8][31] Parahelicoprion is today considered to be a member of the family Helicoprionidae within the monophyletic order Eugeneodontida (alternately spelled Eugeneodontiformes),[4][27] which is itself a member of the subclass Holocephali or Euchondrocephali.[4][32][33] The helicoprionids (described as agassizodontids by some authors)[24] are defined by possessing tooth whorls with forward angled, blade-like tooth crowns and, in many genera, tooth roots which are completely fused. Members of the group also possessed a laterally positioned pavement of flattened crushing teeth. Other aspects of the group's jaws and skull are only rarely preserved, and nothing is known of their postcranial anatomy.[24][4]

Helicoprion bessonowi (left) and Sarcoprion edax (right), both of which are considered close relatives of Parahelicoprion.[4] Exhibit displayed at the Moscow Paleontological Museum

In a 1925 publication, Karpinsky suggested that P. clerci may represent a directly intermediate, transitional form between the "primitive" genus Campodus and the more derived Helicoprion,[21] a conclusion agreed with by Nielsen (1952).[34] Svend Erik Bendix-Almgreem, in a 1976 publication, suggested that Parahelicoprion may have been related to a proposed radiation of whorl-toothed cartilaginous fish unrelated to the helicoprionids and edestids. This lineage was proposed to also consist of Erikodus, Fadenia, and Sarcoprion,[8][24] with P. clerci considered a possible member due to similarities with the latter taxon.[8] Rainer Zangerl (1981) considered Parahelicoprion to be the sister taxon to Campyloprion in his morphological analysis of all (then known) members of the newly proposed order Eugeneodontida, which encompassed the edestids, helicoprionids, and caseodonts.[24] Following Zangerl's analysis, authors Dagmar Merino-Rodo and Phillipe Janvier concluded in their 1986 description of P. mariosuarezi that the genus Parahelicoprion may lack defining derived characteristics, which puts its validity and status as a monophyletic group into question and complicates the matter of assigning new species.[9] In a 2018 publication, paleobotanist Serge Naugholnykh proposes that P. clerci specimens simply represent especially large individuals of Helicoprion and that the two genera are synonymous,[3][26] although subsequent papers have continued to recognize Parahelicoprion as a valid genus of helicoprionid eugeneodont.[18][27][35]

Paleobiology and paleoecology

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Ecology and habitat

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A map of Earth as it appeared during the Cisuralian epoch

Parahelicoprion was a carnivore which inhabited marine environments.[9][10][36] It has been suggested to have been the apex predator of its ecosystem,[3] with the blade-like serrated tooth whorl being adapted for cutting and battering prey.[1][13] While multiple feeding styles are thought to have been present among different genera of edestoids,[29][27] it has been hypothesized that many members of the Helicoprionidae were molluscivorous and fed primarily on ammonoid and coleoid cephalopods,[29][37] with smaller cartilaginous fish potentially constituting a portion of their diet as well.[37]

The teeth of Artiodus prominens, a euselachian stem-group shark known from the Arta Beds of Krasnoufimsk[5]

The Artinskian deposits of Krasnoufimsk, or the Arta Beds, were deposited in a shallow sea basin between the Boreal and Tethys oceans.[3] These fossil beds are made up of the lower (older) Divjinskian or Divya Formation and the upper (younger) Sarginskian Formation, and are composed predominantly of marls and limestones.[3][5][38] During the early Permian, reef habitats made up of bryozoans and rugose corals were present, which were inhabited by a diverse assemblage of trilobites,[5] goniatite and nautiloid cephalopods,[38] and fishes.[3] In addition to Parahelicoprion clerci, the Divya Formation yields a huge variety of chondrichthyan fossils, including the remains of euselachian sharks, hybodonts, symmoriiformes, petalodonts and cochliodonts.[5] The similar helicoprionid Helicoprion bessonowi is also known from numerous tooth whorls collected in the Divya Formation.[3][5]

The Copacabana Formation represented a shallow marine habitat, somewhat older than the Arta Beds and dated to the boundary between the Carboniferous and the Permian. Of the formation's two strata which preserve fish fossils, Parahelicoprion is known only from the upper (younger) layer, while the majority of observed species come from a slightly older layer below it. Among these species, actinopterygians (ray-finned fish) and holocephalans have been identified. The known fossils of holocephalans include remains of the large petalodont similar to Megactenopetalus as well as tooth-plates of cartilaginous fishes similar to Lagarodus or Helodus, both believed to be bottom dwelling, durophagous fishes. Teeth and scales belonging to bony fish in the family Platysomidae are also known, and isolated teeth suggest that cladodont sharks (Identified by Merino-Rodo and Janvier as Cladodus) were also present in the environment.[3][36] The teeth of jawless, fish-like vertebrates called conodonts are abundant, and it is from these index fossils that the age of the formation has been determined. Marine invertebrates have also been found at the site, and include bivalves, brachiopods, trilobites, crinoids and bryozoans. While lower fish-bearing strata of the Copacabana Formation are believed to represent a diverse benthic reef community, Merino-Rodo and Janvier suggest that the sandstones which compose the upper fish-bearing layer and which preserve the whorl of Parahelicoprion may have formed in an even shallower, intertidal habitat, and that the type of P. mariosuarezi represents an animal killed in a stranding.[9] In spite of the difference in time and proposed habitat, Janvier has subsequently described and illustrated the aforementioned species coexisting.[25]

Estimated length

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A high-end length estimate of the closely Helicoprion bessonowi, based on the proportions of caseodonts such as Romerodus and Caseodus. It has been proposed that Parahelicoprion may have exceeded H. bessonowi in size[1]

While the known tooth crowns of the genus are considered to be among the largest of the eugeneodonts; believed to be up to 15 cm (6 in) in height when complete,[39] estimates of Parahelicoprion's total body size have been considered controversial.[40] Karpinsky himself did not provide total length estimates in his 1916 description, but did note that the tooth crowns of P. clerci were very large, and that the animal must have been similarly large to accommodate them.[1] Phillipe Janvier refers to P. mariosuarezi as "huge" in Early Vertebrates (1996),[25] and paleoichthyologist Richard Lund is quoted as saying, in Doug Perrine's 1999 book Sharks and Rays, that Parahelicoprion "... might have been over 30 meters (100 ft) in lengths - perhaps the largest fish of all time", a claim made based on extrapolating size from the preserved section of the whorl.[39] A similar estimate was provided by author and illustrator Richard Ellis in his 2003 book Aquagenesis: The Origin and Evolution of Life in the Sea. Ellis states that, in spite of the poor quality of the known material "... unless it (Parahelicoprion) was an animal with a gigantic head or outlandishly oversized teeth, it had to have been a monster, at least 100 feet long and maybe more." This conclusion was reached based on comparisons between the height of the teeth in Otodus megalodon, which the teeth of Parahelicoprion are said to exceed in size.[13] Length estimates for eugeneodont fishes in excess of 11 meters (36 ft) have not been published in academic, peer-reviewed literature.[40]

Oleg Lebedev, a researcher from the Palaeontological Institute of the Russian Academy of Sciences, estimated in a 2009 publication that the closely related Helicoprion bessonowi may have been between 5-8 meters (16-26 ft) in total body length; a measurement based on assumptions about its head-to-whorl proportions in comparison to the related caseodonts.[40][29] Later studies have proposed a most plausible total length of up to 7 meters (23 ft) for members of the genus Helicoprion and other, similarly large edestoids.[40][41] Due to the fragmentary nature of their fossils, it has been considered unreasonable by some researchers to give precise total length estimates for Helicoprion, Parahelicoprion, or any other members of Edestoidea.[19][40] Though its exact maximum size has not been determined, both species of Parahelicoprion were likely among the largest animals of their respective environments,[3][25] and they and other edestoids likely represented the some of the largest fishes of the Paleozoic era.[32][41][42]

Extinction

[edit]

The latest known occurrence of the genus is the Artinskian stage of the Permian,[5] and it is assumed to have been extinct by the end of the Cisuralian.[35] This may have been due to climatic changes associated with the late Paleozoic ice ages,[40] and Karpinsky has suggested that the disappearance of the seaway connecting the Arctic and Tethys oceans was directly responsible for the extinction of the Uralian edestoids.[1] Alongside Parahelicoprion, many cartilaginous fish genera of the Divya Formation disappear from the fossil record at the close of the Artinskian stage.[5]

See also

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References

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  1. ^ a b c d e f g h i j k l m n o p q r Karpinsky, Alexander Karpinsky (27 April 1916). "On a new species of Helicoprion (Helicoprion clerci, n. sp.)". Bulletin de l'Académie Impériale des Sciences de Saint Pétersbourg (in Russian) (6): 701–708 – via Biodiversity Heritage Library.
  2. ^ a b "Notes". Nature. 98 (2447): 54–55. 21 September 1916 – via Biodiversity Heritage Library.
  3. ^ a b c d e f g h i j k l m Naugolnykh, S.V. (2018). "Artinskian (Early Permian) Sea Basin and Its Biota (Krasnoufimsk, Cis-Urals)". Stratigraphy and Geological Correlation. 26 (7): 734–754. Bibcode:2018SGC....26..734N. doi:10.1134/S0869593818070080. S2CID 135304766.
  4. ^ a b c d e f g h i j k l Ginter, Michał; Hampe, Oliver; Duffin, Christopher J. (2010). Handbook of paleoichthyology: teeth. München: F. Pfeil. ISBN 978-3-89937-116-1.
  5. ^ a b c d e f g h Ivanov, Alexander; Duffin, Christopher; Naugolnykh, Serge (2017). "A new euselachian shark from the Early Permian of the Middle Urals, Russia". Acta Palaeontologica Polonica. 62. doi:10.4202/app.00347.2017. ISSN 0567-7920.
  6. ^ Karpinsky, Alexander (1924). "Helicoprion (Parahelicoprion n.g.) clerci". Bulletin de la Societe Ouralienne des Sciences Naturelles. 34: 1–10.
  7. ^ a b c d e f Karpinsky, Alexander (1922). "Notes on the dental segments of Edestidae and their orientation". Bulletin of the Russian Academy of Sciences (in Russian): 379–388 – via Google Books.
  8. ^ a b c d e f g h Bendix-Almgreen, Svend Erik (1976). "Palaeovertebrate faunas of Greenland". Geology of Greenland. doi:10.22008/GPUB/38226.
  9. ^ a b c d e f g h i j k l m n Merino-Rodo, Dagmar; et al. (1986). "Chondrichthyan and actinopterygian remains from the Lower Permian Copacabana Formation of Bolivia". Geobios. 19 (4): 479–493. Bibcode:1986Geobi..19..479M. doi:10.1016/S0016-6995(86)80005-5.
  10. ^ a b c "PBDB Taxon". paleobiodb.org. Retrieved 15 October 2024.
  11. ^ "Colleciones Cientificas". museonoelkempff.org. Retrieved 11 October 2024.
  12. ^ "para- | Etymology of the prefix para". etymonline.com. Retrieved 22 October 2024.
  13. ^ a b c d e Ellis, Richard (2003). Aquagenesis: the origin and evolution of life in the sea. New York, N.Y: Penguin. ISBN 978-0-14-200156-1.
  14. ^ a b Eastman, C. R. (1900). "Karpinsky's genus Helicoprion: a review". The American Naturalist. 34 (403) – via JSTOR.
  15. ^ a b Ewing, Susan (2017). Resurrecting the shark: a scientific obsession and the Mavericks who solved the mystery a 270 million year old fossil. New York London: Pegasus Books. ISBN 978-1-68177-343-8.
  16. ^ "Para Definition and Meaning". Merriam-Webster. Retrieved 23 October 2024.
  17. ^ Mutter, Raoul J.; Neuman, Andrew G. (2008). "New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada". Geological Society, London, Special Publications. 295 (1): 9–41. doi:10.1144/SP295.3. ISSN 0305-8719.
  18. ^ a b Sansom, Ivan J. (2024-01-24). "Supplementary material from "The skeletal completeness of the Palaeozoic chondrichthyan fossil record"". Royal Society Open Science. doi:10.6084/m9.figshare.c.7041560.v1.
  19. ^ a b Maisey, John G.; Bronson, Allison W.; Williams, Robert R.; McKinzie, Mark (2017-05-04). "A Pennsylvanian 'supershark' from Texas". Journal of Vertebrate Paleontology. 37 (3): e1325369. doi:10.1080/02724634.2017.1325369. ISSN 0272-4634.
  20. ^ a b Baird, Donald (1957). "A Physonemus Spine from the Pennsylvanian of West Virginia". Journal of Paleontology. 31 (5): 1011–1018 – via JSTOR.
  21. ^ a b c Karpinsky, Alexander (1925). "Sur une nouvelle troouvaille de restes de Parahelicoprion et sur relations de ce genre avec Campodus (On a New Find of Remains of Parahelicoprion and on the Relations of This Genus with Campodus)". Soc. Geol. Belg. Livre Jubilaire (in Russian): 125–137.
  22. ^ Lund, Richard (1986-03-07). "On Damocles serratus , nov. gen. et sp. (Elasmobranchii: Cladodontida) from the Upper Mississippian Bear Gulch Limestone of Montana". Journal of Vertebrate Paleontology. 6 (1): 12–19. doi:10.1080/02724634.1986.10011594. ISSN 0272-4634.
  23. ^ Maisey, John G. (2009-03-12). "The spine-brush complex in symmoriiform sharks (Chondrichthyes; Symmoriiformes), with comments on dorsal fin modularity". Journal of Vertebrate Paleontology. 29 (1): 14–24. doi:10.1671/039.029.0130. ISSN 0272-4634.
  24. ^ a b c d e f g h i j k l m n Zangerl, Rainer (1981). Handbook of Paleoichthyology Volume: 3A: Chondrichthyes 1 (1st ed.). Verlag Dr. Friedrich Pfeil. pp. 74–94. ISBN 978-3899370454.
  25. ^ a b c d Janvier, Philippe (1996). Early vertebrates. Oxford science publications. Oxford : New York: Clarendon Press ; Oxford University Press. p. 22. ISBN 978-0-19-854047-2.
  26. ^ a b Наугольных, с.в.; Наумкин, д.в. (2023). "ПАЛЕОЭКОЛОГИЯ И ПАЛЕОИХНОЛОГИЯ НИЖНЕПЕРМСКИХ ОТЛОЖЕНИЙ РАЙОНА Г. КРАСНОУФИМСК (СВЕРДЛОВСКАЯ ОБЛ.)". Горное эхо (in Russian) (4): 19–38. doi:10.7242/echo.2023.4.3. ISSN 2658-5227.
  27. ^ a b c d Lebedev, Oleg A.; Itano, Wayne M.; Johanson, Zerina; Alekseev, Alexander S.; Smith, Moya M.; Ivanov, Aleksey V.; Novikov, Igor V. (2022). "Tooth whorl structure, growth and function in a helicoprionid chondrichthyan Karpinskiprion (nom. nov.) (Eugeneodontiformes) with a revision of the family composition". Earth and Environmental Science Transactions of The Royal Society of Edinburgh. 113 (4): 337–360. doi:10.1017/S1755691022000251. ISSN 1755-6910.
  28. ^ Bendix-Almgreen, Svend Erik (1966). "New investigations on Helicoprion from the Phosphoria Formation of south-east Idaho" (PDF). Biol. Skrifter Udgivet Af Det Kongelige Danske Videnskabernes Selskab. 14 (5): 1–54.
  29. ^ a b c d Lebedev, O. A. (2009). "A new specimen of Helicoprion Karpinsky, 1899 from Kazakhstanian Cisurals and a new reconstruction of its tooth whorl position and function". Acta Zoologica. 90 (s1): 171–182. doi:10.1111/j.1463-6395.2008.00353.x. ISSN 0001-7272.
  30. ^ Tapanila, Leif; Pruitt, Jesse (2013). "Unraveling species concepts for the Helicoprion tooth whorl". Journal of Paleontology. 87 (6): 965–983. doi:10.1666/12-156. ISSN 0022-3360.
  31. ^ Moy-Thomas, J. A.; Miles, Roger S. (1971). Palaeozoic fishes (2d ed., extensively rev ed.). Philadelphia: Saunders. ISBN 978-0-7216-6573-3.
  32. ^ a b Tapanila, Leif; Pruitt, Jesse; Wilga, Cheryl D.; Pradel, Alan (2020). "Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition". The Anatomical Record. 303 (2): 363–376. doi:10.1002/ar.24046. ISSN 1932-8486.
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