Romerodus

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Romerodus
Temporal range: Pennsylvanian (Moscovian-Kasimovian), 307-304 Ma
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Possible Early Permian record
Romerodus skeletal.png
Skeletal reconstruction of R. orodontus, with well described material in white and preserved but poorly defined material in gray. The body outline as shown represents the extent of phosphatized skin.
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Holocephali
Order:† Eugeneodontida
Family:† Caseodontidae
Genus:† Romerodus
Zangerl, 1981
Type species
Romerodus orodontus
Zangerl, 1981

Romerodus is an extinct genus of cartilaginous fish in the family Caseodontidae. While it and the rest of its family were historically considered elasmobranchs related to sharks and rays, they are now regarded as holocephalans, a diverse subclass which is today only represented by chimaeras. Romerodus is known from the Carboniferous and possibly Permian periods of North America, and the only named species, R. orodontus, was discovered in organic shale deposits in the U.S. state of Nebraska. It is one of few members of its order, the Eugeneodontida, that is known from multiple complete, well preserved body fossils, and is thus an important taxon for understanding the anatomy and ecology of less well preserved eugeneodonts such as Helicoprion . The genus name honors paleontologist Alfred Romer.

Contents

The body of R. orodontus was similar to that of other caseodontids. It possessed a slender, streamlined profile, a strongly keeled crescent-shaped caudal fin, and proportionally very small dorsal and pectoral fins. Unlike modern sharks and rays, there is no indication Romerodus possessed pelvic fins or claspers. Its teeth were smoother and less ornamented than those of other caseodonts, and were positioned in tightly-packed rows. It inhabited deep-water marine environments, and like its relatives shows adaptations associated with life as a pelagic carnivore. Unlike its larger relatives, however, the largest known Romerodus were approximately 50 cm (20 in) in total length.

Discovery and naming

Romerodus orodontus was named and described in 1981 by paleontologist Rainer Zangerl based on multiple crushed (but otherwise well-preserved) body fossils. [1] R. orodontus lived between 307–304 million years ago, [2] during the latest Moscovian to Kasimovian stages (described by Zangerl as the equivalent Westphalian D substage) [1] of the Pennsylvanian subperiod. [3] [4] [5] All described specimens originated from the Hansen Quarry, which is located in Sarpy County, Nebraska. The strata which produced these Romerodus fossils are part of the Stark Shale Member of the Dennis Formation and Wea Shale Member of the Cherryville Shale Formation, [6] [7] [3] and are described as fissile, black, and organic. [5] [8] : 238–239 

The incomplete but articulated specimen FMNH PF 8522 from the Stark Shale is designated as the holotype of the genus and species, and consists of the front half of the animal preserved in ventral (bottom) view. [1] [7] Alongside the incomplete holotype, eight assigned paratype specimens were included in the initial description, from which the complete anatomy can be observed. [1] The holotype and paratypes are housed at the Field Museum of Natural History, [7] with additional known specimens now being part of private collections. [9] The genus name honors the influential vertebrate paleontologist Alfred Romer, [1] whose surname is used in combination with the Greek suffix -odus (ὀδούς) which translates as 'tooth'. [10] The species name, orodontus, may be translated as either 'beautiful tooth' [11] or 'mountain tooth'. [10]

Isolated teeth referred to as "cf. Romerodus sp." have been identified from the Early Permian Phosphoria Formation, in exposed limestone deposits in what are now Grand Teton and Yellowstone national parks. The condition of fossils recovered from these localities is poor due to extensive weathering, and they have not been described in detail. [12]

Description

Life reconstruction of Romerodus, based primarily on a large specimen in the collection of Rene Kindlimann Romerodus.png
Life reconstruction of Romerodus, based primarily on a large specimen in the collection of René Kindlimann

Examples of articulated specimens assigned to Romerodus are preserved in both ventral (underside) and lateral (profile) views. [7] [8] : 238–239  [9] The phosphatized remains consist of the animal's full body outline and skin, along with detailed preservation of the ossified cartilage of the lower jaws and pectoral region, and the delicate pterygiophores and ceratotrichia which supported the pectoral fins. [8] : 238–239  [9] The maximum total length of R. orodontus is stated to be approximately 50 cm (20 in), [6] although a specimen of indeterminate species in the collection of René Kindlimann has been measured at 56 cm (22 in) in length. [9]

Body and fins

The appearance of Romerodus was typical of a caseodontid. [6] [13] The gill arches may have supported either separated, shark-like gill slits or a single chimaera-like operculum (gill cover). [13] [14] : 143–144, 167  According to Zangerl's 1981 description, the profile was fusiform, with a forked, homocercal caudal fin and greatly enlarged keels on the caudal peduncle. [1] No specimens show any indication of pelvic fins, a pelvic girdle, or claspers, [1] suggesting that these structures were either greatly reduced or absent in life. [6] [14] : 167–169  Neither a second dorsal fin nor fin spine has been identified, [1] [15] as in other eugeneodonts. [1]

Unlike its larger relatives, many elements of Romerodus' skeleton were strongly calcified, with the exceptions of the vertebral centra and the radials of the dorsal fin. [1] This single dorsal fin was supported by a plate of fused basal cartilage and was positioned above the pectoral girdle. The pectoral fins were proportionally very small. [1] [6] As in its closest relatives, the chevrons and neural arches of the caudal (tail) fin's upper lobe were broad and greatly fused. [1] [6] This condition is in contrast with eugeneodontids such as Eugeneodus and is most similar to that seen in Fadenia and Caseodus. [1] [13] The scapulocoracoids (pectoral girdle) were well-developed but unfused, similar to those of many other Paleozoic chondrichthyans. Below the pectoral girdles were paired, sternal cartilages of unknown function, [1] which may have been homologous to the unpaired sternum-like structure observed in the related Ornithoprion and Fadenia. [1] [13]

Teeth

Unlike other eugeneodonts such as Agassizodus (pictured), Romerodus lacked "buttress-like" ridges along the crowns of its pavement teeth Agassizodus.jpg
Unlike other eugeneodonts such as Agassizodus (pictured), Romerodus lacked "buttress-like" ridges along the crowns of its pavement teeth

Michal Ginter and coauthors have described information on the dentition of Romerodus as "sparse". [6] As in other eugeneodonts, the teeth of R. orodontus formed a pavement-like dentition (broad, flattened, and overlapping), although its roots uniquely lacked deep crenulations and its crowns lacked the "buttress-like" ridges seen in the pavement teeth of many other caseodonts. Among eugeneodonts and the potentially related orodonts, the pavement teeth were typically arranged in tightly-packed lateral rows along both the upper and lower jaws. [1] [6] Also as in other eugeneodonts, Romerodus bore a whorl of teeth along the midline, or symphysis, of the lower jaw. The symphyseal tooth whorl of R. orodontus was roughly 25% of the length of the skull, making it proportionally shorter than that of other measured caseodonts, in which it ranges from 28–40% of the skull's length. [16]

Classification

The morphologically similar caseodont Caseodus (pictured) has been considered the closest relative of Romerodus Caseodus cropped.png
The morphologically similar caseodont Caseodus (pictured) has been considered the closest relative of Romerodus

When initially described, Romerodus was assigned to the subclass Elasmobranchii, a group of cartilaginous fish which includes true sharks and their relatives and which Zangerl believed included the eugeneodonts as well. [1] [17] Recent findings, however, strongly suggest that the order Eugeneodontida, to which Romerodus belongs, are a lineage of holocephalan (also defined as euchondrocephalan) fish distantly related to living chimaeras. [6] [18] This classification is based on the suspension of the jaw in eugeneodonts, termed autodiastylic, which is distinctive of early euchondrocephalans. [19] [20] The histology of the teeth, which in some genera are composed of trabecular dentin (a distinctive form of dentin found in holocephalans) [17] has also supported a relation with this group. [21] Despite their evolutionary proximity to chimaeras, eugeneodonts converged on a similar body and tooth morphology to sharks due to shared ecology. [20]

The Eugeneodontida is subdivided into the Edestoidea and Caseodontoidea suborders based on differences in the structure of the symphyseal tooth whorl, with Romerodus representing a member of the latter and, more specifically, a member of the family Caseodontidae. [1] [6] [18] Rainer Zangerl's morphological analysis of the group, published in 1981, indicates that R. orodontus is most closely related to Caseodus based on similarities in dentition, as well as the structure of their tails and upper jaws. The postcranial anatomy of the caseodonts was apparently extremely conserved and varied little between genera, although features in their skulls and teeth indicate they were an ecologically diverse group. [6] The phylogeny of the Eugeneodontida as presented in Zangerl (1981) is provided below. [1]

Paleoecology

Romerodus (center) alongside Agassizodus (top) and Listracanthus (bottom), all of which inhabited the Midcontinent Sea during the late Pennsylvanian Listracanthus hystrix.JPG
Romerodus (center) alongside Agassizodus (top) and Listracanthus (bottom), all of which inhabited the Midcontinent Sea during the late Pennsylvanian

The Stark Shale, where the type specimen of R. orodontus originated, is believed to have been a marine depositional environment. [2] [22] During the Late Carboniferous, Nebraska was part of the Late Pennsylvanian Midcontinent Sea; a deep, inland sea which was rich in phosphates and organic material. [23] The Stark Shale has been interpreted as a deep-water, offshore habitat with a cold, anoxic (lacking oxygen) bottom created by a strong thermocline (temperature gradient) and halocline (salinity gradient). [5] [24] Upwellings would have caused nutrient-rich conditions in the upper water column, encouraging the growth of algae and other plankton which, as they died, would be deposited on the oxygen-poor seafloor to form shale. [23] [24] The Wea Shale is also considered to represent an offshore marine environment with comparable preservational conditions, [25] although it was likely deposited in shallower waters. [3] In black shales such as the Stark and Wea, benthic fauna is rare. [23] Fossils of benthic animals have been proposed to have originated from more habitable environments or to represent individuals which became detached from floating debris. [24] [26] It is theorized that most of the species preserved at the site were pelagic and lived high in the water column. The pelagic animals then sank to the anoxic seabed after death, where they were preserved in exceptional detail due to the lack of decomposers and scavengers. [23] [25] The conditions observed in these mid-continent shales are associated with warmer interglacial periods during the late Paleozoic ice age. [23]

The Stark and Wea shales preserve a variety of other fishes in addition to Romerodus, including some of the most complete cartilaginous fish specimens known from the Paleozoic. [3] [25] These include Cobelodus , [8] : 228–232  Heslerodus , [27] Listracanthus, [8] : 243  [26] several species of well-preserved iniopterygian, [25] [28] and other eugeneodonts such as Gilliodus , [1] Agassizodus, and indeterminate genera known only from a pectoral fin or isolated tooth whorls. [8] : 237  Conodonts and paleoniscoid fishes are also known, [23] [8] : 285–287 with the conodont variety providing further evidence of a deep, stratified water column with multiple faunal communities at varying levels. [24] The known invertebrate fossils of the Stark and Wea shales include jellyfish, brachiopods, crinoids, bryozoans, [3] and multiple species of tyrannophontid, [3] [26] including the genus Gorgonophontes . It has been proposed that these crustaceans, which are found only in isolated regions, may have been part of a poorly known benthic fauna which was adapted to oxygen-poor deep waters, or alternatively originated from die-offs in a shallower ecosystem nearby. [26] Multiple species of small, ink-producing coleoids are known from the Stark Shale, as well as several kinds of ammonoid. [5]

Tooth-whorl of Sinohelicoprion, collected from the Phosphoria Formation of Grand Teton National Park Sinohelicoprion sp.jpg
Tooth-whorl of Sinohelicoprion, collected from the Phosphoria Formation of Grand Teton National Park

The Permian Phosphoria Formation, in which Romerodus may occur, also preserves a diverse assemblage of chondrichthyans. Fossils discovered at the Yellowstone and Grand Teton exposures are often heavily weathered, however, making precise identification of taxa difficult. The deposits which yield Romerodus-like fish are limestones preserving large numbers of unassociated teeth, bones, and fin spines from different species collected together, which may represent mass-death assemblages. Among the genera confidently identified at these sites are Glikmanius , Deltodus , and a rare North American occurrence of the otherwise Asian genus Sinohelicoprion . The site has also yielded examples of platysomids, cochliodonts, petalodonts and orodonts, although many of these have not been identified confidently to the genus level. [12]

Paleobiology and significance

In life Romerodus was, as has been proposed for all eugeneodonts, an active, nektonic carnivore, [2] and it is assumed to have been a very powerful swimmer. [16] Russell Engelmann, in a 2024 paper, proposes that aspects of eugeneodont anatomy such as the greatly reduced or absent pelvic fins, forked caudal fin, and streamlined body are adaptations associated with a pelagic lifestyle among other living and extinct fishes. [29] The lifeless, anoxic conditions proposed for the seabed of the Stark and Wea shales further suggest that R. orodontus lived high in the water column. [23] [26]

General trends associated with a pelagic lifestyle among fishes, as proposed in Engelmann (2024). Eugeneodontida were cited as an example of a lineage which shows pelagic adaptations Scombrid morphological optima.jpg
General trends associated with a pelagic lifestyle among fishes, as proposed in Engelmann (2024). Eugeneodontida were cited as an example of a lineage which shows pelagic adaptations
Reconstruction of a very large Helicoprion, based partially on the postcranial anatomy of R. orodontus Helicoprion skeletal.jpg
Reconstruction of a very large Helicoprion, based partially on the postcranial anatomy of R. orodontus

Thanks to its well preserved body fossils, Romerodus has been used to approximate the size, proportions, and anatomy of the distantly related and more widely publicized genus Helicoprion. [14] : 115  [30] Postcranial remains of edestoids, the suborder to which Helicoprion belongs, are entirely unknown, [6] leaving caseodonts as the closest analogues to bracket their anatomy. Directly scaling the cranial and postcranial proportions of Romerodus and its close relatives indicates the largest known Helicoprion individuals may have been between 7 to 11 m (23 to 36 ft) in length, [16] [30] although such estimates rely on the notion that both fish were close in ecology and phylogenetic position. [30] Due to its short jaws and proportionally large tooth whorl, however, Helicoprion may have been more anatomically different from caseodonts than previously assumed, [19] and a subsequent publication has suggested lengths around 7 m (23 ft) are likely the most reasonable. [30] The Idaho Museum of Natural History displayed murals and a life-sized replica of Helicoprion davidsii, [31] which featured body proportions and anatomy inspired by well preserved caseodonts such as Romerodus. The paintings and design of the animal were realized by Alaskan illustrator Ray Troll and sculptor Gary Staab. [14] : 169 

See also

Related Research Articles

<span class="mw-page-title-main">Chondrichthyes</span> Class of jawed cartilaginous fishes

Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opercula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.

<span class="mw-page-title-main">Holocephali</span> Subclass of cartilagenous fish

Holocephali, sometimes given the name Euchondrocephali, is a subclass of cartilaginous fish in the class Chondrichthyes. The earliest fossils are of teeth and come from the Devonian period. Little is known about these primitive forms, and the only surviving group in the subclass is the order Chimaeriformes.

<i>Cladoselache</i> Extinct genus of chondrichthyans

Cladoselache is an extinct genus of shark-like chondrichthyan from the Late Devonian (Famennian) of North America. It was similar in body shape to modern lamnid sharks, but was not closely related to lamnids or to any other modern (selachian) shark. As an early chondrichthyan, it had yet to evolve traits of modern sharks such as accelerated tooth replacement, a loose jaw suspension, enameloid teeth, and possibly claspers.

<i>Helicoprion</i> Genus of fossil fishes

Helicoprion is an extinct genus of shark-like eugeneodont 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. Fossils of Helicoprion are known from a 20 million year timespan during the Permian period from the Artinskian stage of the Cisuralian to the Roadian stage of the Guadalupian. The closest living relatives of Helicoprion are the chimaeras, though their relationship is very distant. 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. 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.

<i>Stethacanthus</i> Extinct genus of cartilaginous fishes

Stethacanthus is an extinct genus of shark-like cartilaginous fish which lived from the Late Devonian to Late Carboniferous epoch, dying out around 298.9 million years ago. Fossils have been found in Australia, Asia, Europe and North America.

<i>Cobelodus</i> Extinct genus of cartilaginous fishes

Cobelodus is an extinct genus of cartilaginous fish known from the late Carboniferous to the early Permian period. The type specimen, assigned to the genus Styptobasis, was discovered by Edward Drinker Cope in Illinois Basin black coal shales. Rainer Zangerl reassigned S. aculeata in 1973 to the genus Cobelodus, translating to 'needle tooth'. Cope's description was based from a tooth fragment and was compared to the genus Monocladodus. Cobelodus differs from Styptobasis and Monocladodus in the anatomy of its teeth and pectoral fins.

<i>Edestus</i> Extinct genus of eugeneodontid fish

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 midline of the upper and lower jaws. Edestus is a Greek name derived from the word edeste, 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, possibly making it the largest marine predator to have ever existed up to that point.

<span class="mw-page-title-main">Stethacanthidae</span> Extinct family of cartilaginous fishes

Stethacanthidae is an extinct family of prehistoric holocephalians. It is estimated to have existed approximately between 380 and 300 million years ago. Members of this family are noted for their peculiar dorsal fin.

<i>Sarcoprion</i> Extinct genus of cartilaginous fish

Sarcoprion is an extinct genus of eugeneodont holocephalan from the Permian of Greenland. Similar to other helicoprionids such as Agassizodus and Helicoprion, it possessed tooth whorls on the symphysis of the jaw as well as flattened, pavement-type teeth. It is distinguished from other members of its family by the presence of sharp, symphyseal teeth on both the upper and lower jaws. The tooth whorl on the lower jaw bore sharp, compact tooth crowns, while a row of backward facing, triangular teeth was present on the roof of the mouth. The preserved material does not show evidence of a distinct upper jaw, implying it may have been fused to the cranium, reduced, or lost entirely. The type and only species in the genus is S. edax.

<i>Campodus</i> Extinct genus of sharks

Campodus is an extinct genus of eugeneodont holocephalans from the Carboniferous. Likely one of the earliest and most basal caseodontoids, it can be characterized by its broad, ridge-ornamented crushing teeth made of various types of dentine. The type species, C. agassizianus, was originally described in 1844 based on a small number of teeth from the Namurian of Belgium.

<i>Fadenia</i> Extinct genus of sharks

Fadenia is an extinct genus of eugeneodontid holocephalian chondrichthyan from the Carboniferous Period of Missouri, the Permian period of Greenland, and the Early Triassic epoch of British Columbia, Canada.

<i>Parahelicoprion</i> Extinct genus of cartilaginous fish

Parahelicoprion is an extinct genus of shark-like cartilaginous fish that lived during the Early Permian. Two species are known ; P. clerci from Arta Beds of the Ural Mountains of Russia, and P. mariosuarezi from 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, another eugeneodont from the Ural Mountains that bore a similar midline tooth arrangement.

<span class="mw-page-title-main">Eugeneodontida</span> Extinct order of cartilaginous fishes

The Eugeneodontida, sometimes also called Eugeneodontiformes, is an extinct and poorly known order of cartilaginous fishes. They possessed "tooth-whorls" on the symphysis of either the lower or both jaws and pectoral fins supported by long radials. They probably lacked pelvic fins and anal fins. The palatoquadrate was either fused to the skull or reduced. Now determined to be within the Holocephali, their closest living relatives are chimaeras. The eugeneodonts are named after paleontologist Eugene S. Richardson, Jr. The group first appeared in the fossil record during the late Mississippian (Serpukhovian). The youngest eugeneodonts are known from the Early Triassic. The geologically youngest fossils of the group are known from the Sulphur Mountain Formation, Vardebukta Formation and Wordie Creek Formation (Greenland).

<span class="mw-page-title-main">Helicoprionidae</span> Family of fossil fish

Helicoprionidae is an extinct family of holocephalids within the order Eugeneodontida. Members of the Helicoprionidae possessed a unique "tooth-whorl" on the symphysis of the lower jaw and pectoral fins supported by long radials. The closest living relatives of the Helicoprionidae and all other eugeneodontids are the ratfishes. The anatomy of the tooth-whorl differed amongst genus and species, some possessing complete spirals, others possessing halved spirals, and some with wedged half-spirals. Each tooth-whorl is thought to be adapted to a different type of prey, and a different predation strategy.

<span class="mw-page-title-main">Iniopterygiformes</span> Extinct order of sharks

Iniopterygiformes is an extinct order of chimaera-like cartilaginous fish that lived from the Devonian to Carboniferous periods. Fossils of them have been found in Montana, Indiana, Illinois, and Nebraska. The Iniopterygians are characterized by large pectoral fins, wing-like projections on their backs, mounted high on the body and denticulated bony plates on the head and jaws. Iniopterygian sharks were small, and their average length was about 18 inches (46 cm). The elongated pectoral fins had denticles along the leading edge which may have had a role in mating. They are thought to have been able to move their pectorals in a vertical plane, ”flying” through the water much like modern-day flying fish.

Toxoprion is an extinct genus of eugeneodont holocephalans whose fossils are found in marine strata from the Early Carboniferous until the Late Permian near Eureka, Nevada.

<i>Ornithoprion</i> Extinct genus of cartilaginous fishes

Ornithoprion is a genus of extinct cartilaginous fish in the family Caseodontidae. The only species, O. hertwigi, lived during the Moscovian stage of the Pennsylvanian, between 315.2 to 307 million years ago, and is known from black shale deposits in what is now the Midwestern United States. The discovery and description of Ornithoprion, performed primarily via radiography, helped clarify the skull anatomy of eugeneodonts; a group which includes O. hertwigi and which were previously known primarily from isolated teeth. The genus name, which is derived from the ancient Greek órnith- meaning 'bird' and príōn meaning 'saw', was inspired by the animal's vaguely bird-like skull and the saw-like appearance of the lower teeth. The species name honors Oscar Hertwig.

<i>Agassizodus</i> Extinct genus of sharks

Agassizodus is an extinct genus of eugeneodont holocephalian from the Carboniferous. It belongs to the family Helicoprionidae, which is sometimes called Agassizodontidae. Like other members of its family, it possessed a symphyseal tooth whorl, which was likely present at the tip of the lower jaw and associated with lateral crushing toothplates. The type species, A. variabilis, was originally named Lophodus variabilis until the name "Lophodus" was determined to be preoccupied.

<i>Dracopristis</i> Extinct genus of cartilaginous fishes

Dracopristis is an extinct genus of ctenacanth that lived around 307 million years ago during the Pennsylvanian subperiod of the Carboniferous period. A single species is known, Dracopristis hoffmanorum, which is named in honor of Ralph and Jeanette Hoffman.

<i>Paredestus</i> Extinct genus of cartilaginous fish

Paredestus is a monotypic genus of extinct eugeneodont holocephalan from the Early Triassic of Canada. The type and only species, P. bricircum represents the last known member of the superfamily Edestoidea and among the last known eugeneodonts. It was named in 2008 based on tooth and jaw material, with the holotype representing the only known specimen.

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  15. ↑ Itano, Wayne M.; Houck, Karen J.; Lockley, Martin G. (2003). "Ctenacanthus and other chondrichthyan spines and denticles from the Minturn Formation (Pennsylvanian) of Colorado". Journal of Paleontology. 77 (3): 524–535. doi:10.1017/S002233600004422X. ISSN   0022-3360.
  16. 1 2 3 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.
  17. 1 2 Zangerl, Rainer; Zangerl, Rainer (1966). A new shark of the family Edestidae, Ornithoprion hertwigi, from the Pennsylvanian Mecca and Logan quarry shales of Indiana. [Chicago]: Field Museum of Natural History. pp. 31–35. doi:10.5962/bhl.title.5302.
  18. 1 2 Nelson, Joseph S.; Grande, Terry; Wilson, Mark V. H. (2016). Fishes of the world (5th ed.). Hoboken, New Jersey: John Wiley & Sons. pp. 48–50. ISBN   978-1-119-22081-7.
  19. 1 2 Tapanila, Leif; Pruitt, Jesse; Pradel, Alan; Wilga, Cheryl D.; Ramsay, Jason B.; Schlader, Robert; Didier, Dominique A. (2013-04-23). "Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion". Biology Letters. 9 (2): 20130057. doi:10.1098/rsbl.2013.0057. ISSN   1744-9561. PMC   3639784 . PMID   23445952.
  20. 1 2 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. PMID   30536888.
  21. ↑ Moy-Thomas, J. A. (1971), "Subclass Chondrichthyes. Infraclass Holocephali", Palaeozoic Fishes, Boston, MA: Springer US, pp. 226–245, doi:10.1007/978-1-4684-6465-8_10, ISBN   978-1-4684-6467-2 , retrieved 2024-10-21
  22. ↑ "PBDB Taxon" . Retrieved 7 September 2024.
  23. 1 2 3 4 5 6 7 Heckel, Philip H. (2008), "Pennsylvanian cyclothems in Midcontinent North America as far-field effects of waxing and waning of Gondwana ice sheets", Special Paper 441: Resolving the Late Paleozoic Ice Age in Time and Space, vol. 441, Geological Society of America, pp. 275–289, doi:10.1130/2008.2441(19), ISBN   978-0-8137-2441-6 , retrieved 2024-10-01
  24. 1 2 3 4 Heckel, Phillip H. (1977). "Origin of Phosphatic Black Shale Facies in Pennsylvanian Cyclothems of Mid-Continent North America". AAPG Bulletin. 61. doi:10.1306/C1EA43C4-16C9-11D7-8645000102C1865D. ISSN   0149-1423.
  25. 1 2 3 4 Schnetz, Lisa; Butler, Richard J.; Coates, Michael I.; Sansom, Ivan J. (2024). "The skeletal completeness of the Palaeozoic chondrichthyan fossil record". Royal Society Open Science. 11 (1): 14–17. doi:10.1098/rsos.231451. ISSN   2054-5703. PMC   10827434 . PMID   38298400.
  26. 1 2 3 4 5 Schram, Fredrick R. (1 January 1984). "Frederick R. Schram; Upper Pennsylvanian arthropods from black shales of Iowa and Nebraska". Journal of Paleontology. 1: 197–209. JSTOR   1304745 – via JSTOR.
  27. ↑ "Collection: Hansen Quarry, Quarry 6, Stark Shale, Papillion Sarpy County, Nebraska, USA". mindat.org. Retrieved 1 October 2024.
  28. ↑ Zangerl, Rainer; Case, Gerard R. (1973). Iniopterygia : a new order of Chondrichthyan fishes from the Pennsylvanian of North America. Fieldiana. Vol. 6. Chicago: Field Museum of Natural History. doi:10.5962/bhl.title.5158.
  29. ↑ Engelman, Russell K. (2024-09-07). "Reconstructing Dunkleosteus terrelli (Placodermi: Arthrodira): A new look for an iconic Devonian predator". Palaeontologia Electronica. 27 (3): 1–79. doi: 10.26879/1343 . ISSN   1094-8074.
  30. 1 2 3 4 Gayford, Joel H.; Engelman, Russell K.; Sternes, Phillip C.; Itano, Wayne M.; Bazzi, Mohamad; Collareta, Alberto; Salas-Gismondi, Rodolfo; Shimada, Kenshu (3 September 2024). "Cautionary tales on the use of proxies to estimate body size and form of extinct animals". Ecology and Evolution. 14 (9): e70218. Bibcode:2024EcoEv..1470218G. doi:10.1002/ece3.70218. ISSN   2045-7758. PMC   11368419 . PMID   39224151.
  31. ↑ Taylor, Andrew (5 December 2019). "Idaho Museum of Natural History's buzzsaw sharks featured story in December National Geographic Magazine". isu.edu. Retrieved 28 October 2024.
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