Hybodontiformes

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Hybodontiformes
Temporal range: 360.7–66  Ma
Asteracanthus image.jpg
Fossil and life restoration of Asteracanthus , from the Late Jurassic of Europe
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Infraclass: Euselachii
Order:† Hybodontiformes
Patterson, 1966
Families

See text

Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like cartilaginous fish (chondrichthyans) which existed from the late Devonian to the Late Cretaceous. Hybodonts share a close common ancestry with modern sharks and rays (Neoselachii) as part of the clade Euselachii. They are distinguished from other chondrichthyans by their distinctive fin spines and cephalic spines present on the heads of males. An ecologically diverse group, they were abundant in marine and freshwater environments during the late Paleozoic and early Mesozoic, but were rare in open marine environments by the end of the Jurassic, having been largely replaced by modern sharks, though they were still common in freshwater and marginal marine habitats. They survived until the end of the Cretaceous, before going extinct.

Contents

Etymology

The term hybodont comes from the Greek word ὕβος or ὑβός meaning hump or hump-backed and ὀδούς, ὀδοντ meaning tooth. This name was given based on their conical compressed teeth.

Taxonomic history

Hybodonts were first described in the nineteenth century based on isolated fossil teeth (Agassiz, 1837). Hybodonts were first separated from living sharks by Zittel (1911). [1] Although historically argued to have a close relationship with the modern shark order Heterodontiformes, this has been refuted. [2] Hybodontiformes are total group-elasmobranchs and the sister group to Neoselachii, which includes modern sharks and rays. Hybodontiformes and Neoselachii are grouped together in the clade Euselachii, to the exclusion of other total-group elasmobranchs like Xenacanthiformes. [3] Hybodonts are divided into a number of families, but the higher level taxonomy of hybodonts, especially Mesozoic taxa, is poorly resolved. [4]

Description

Specimen of "Hybodus" fraasi from the Late Jurassic of Germany, which some studies have included in Egertonodus Hybodus fraasi (fossil).jpg
Specimen of "Hybodus" fraasi from the Late Jurassic of Germany, which some studies have included in Egertonodus
Skeletal diagram of Hybodus sp. Hybodusskeeletal4 wikipedia.png
Skeletal diagram of Hybodus sp.

The largest hybodonts reached lengths of 2–3 metres (6.6–9.8 ft), [4] while some other hybodonts were much smaller, with adult body lengths of around 25 centimetres (0.82 ft). [5] Hybodonts had a generally robust bodyform. Due to their cartilaginous skeletons usually disintegrating upon death like other chondrichthyans, hybodonts are generally described and identified based on teeth and fin spine fossils, which are more likely to be preserved. [4] Rare partial or complete skeletons are known from areas of exceptional preservation. [6] [4] [7]

Restoration of Hybodus hauffianus showing sexual dimorphism with fin claspers and cephalic spines present in males (below) but absent in females (above) Hybodus hauffianus.png
Restoration of Hybodus hauffianus showing sexual dimorphism with fin claspers and cephalic spines present in males (below) but absent in females (above)

Hybodonts are recognized as having teeth with a prominent cusp which is higher than lateral cusplets. [8] Hybodont teeth are often preserved as incomplete fossils because the base of the tooth is not well attached to the crown. [8] Hybodonts were initially divided into two groups based on their tooth shape. [9] One group had teeth with acuminate cusps that lacked a pulp cavity; these are called osteodont teeth. The other group had a different cusp arrangement and had a pulp cavity, these are called orthodont teeth. [10] For example, the hybodont species Heterophychodus steinmanni have osteodont teeth with vascular canals of dentine which are arranged vertically parallel to each other, also called ‘tubular dentine’. [11] The crowns of these osteodont teeth are covered with a single layer of enameloid. Hybodont teeth served a variety of functions depending on the species, including grinding, crushing (durophagy), tearing, clutching, and even cutting. [4]

Hybodonts are characterized by having two dorsal fins each preceded by a fin spine. The fin spine morphology is unique to each hybodont species. The fin spines are elongate and gently curved towards the rear, with the posterior part of the spine being covered in hooked denticles, typically in two parallel rows running along the length of the spine, sometimes with a ridge between them. Part of the front of the spines are often covered in a ribbed ornamentation, while in some other hybodonts this region is covered in rows of small bumps. The spines are mineralised, and primary composed of osteodentine, while the ornamentation is formed of enamel. [12] Similar fin spines are also found in many extinct chondrichthyan groups as well as in some modern sharks like Heterodontus and squalids. [13] Male hybodonts had either one or two pairs of cephalic spines on their heads, a characteristic distinctive to hybodonts. [14] These spines, while of variable placement, [10] were always placed posterior to the eye socket, [15] and were composed of a base divided into three lobes, with the main part of the spine being backwardly curved, most specimens of which had a barb near the apex. [10] These spines, like the fin spines, were mineralised, with the base composed of osteodentine, [16] while the main part of the spine was covered in enamel. Male hybodonts possessed fin claspers used in mating, like modern sharks. [10] Hybodonts had a fully heterocercal tail fin, where the upper lobe of the fin was much larger than the lower one due to the spine extending into it. [17] Like living sharks and rays, the skin of hybodonts was covered with dermal denticles. [18] Hybodonts laid egg cases, similar to those produced by living cartilaginous fish. Most hybodont egg cases are assigned to the genus Palaeoxyris, which tapers towards both ends, with one end having a tendril which attached to substrate, with the middle section being composed of at least three twisted bands. [19]

Ecology

Hybodont egg cases (Palaeoxyris) attached to a Neocalamites stem in an estuarine environment. Art by Michael Rothman Sgff a 1907442 f0011 c.jpg
Hybodont egg cases ( Palaeoxyris ) attached to a Neocalamites stem in an estuarine environment. Art by Michael Rothman

Hybodont fossils are found in depositional environments ranging from marine to fluvial (river deposits). [20] Many hybodonts are thought to have been euryhaline, able to tolerate a wide range of salinities. [21] Hybodonts inhabited freshwater environments from early in their evolutionary history, spanning from the Carboniferous onwards. [22] Based on isotopic analysis, some species of hybodonts are likely to have permanently lived in freshwater environments, [23] [24] while others may have migrated between marine and freshwater environments. [25] [26] One genus of hybodont, Onychoselache of the lower Carboniferous of Scotland, is suggested to have been capable of amphibious locomotion, similar to modern orectolobiform sharks such as bamboo and epaulette sharks, due to its well-developed pectoral fins. [16] It has been suggested that male hybodonts used their cephalic spines to grip females during mating. [27] Preserved egg cases of hybodonts assigned to Palaeoxyris indicate that at least some hybodonts laid their eggs in freshwater and brackish environments, with the eggs being attached to vegetation via a tendril. Laying of eggs in freshwater is not known in any living cartilaginous fish. [28] [19] [29] At least some hybodonts are suggested to have utlilized specific sites as nurseries, such as in the Triassic lake deposits of the Madygen Formation of Kyrgyzstan, where eggs of Lonchidion are suggested to have been laid on the lakeshore or upriver areas, where the juveniles hatched and matured, before migrating deeper into the lake as adults. [28]

Life restoration of Strophodus rebecae with other contemporary organisms from the Early Cretaceous (Valanginian-Hauterivian) Rosa Blanca Formation of Colombia Strophodus rebecae.png
Life restoration of Strophodus rebecae with other contemporary organisms from the Early Cretaceous (Valanginian-Hauterivian) Rosa Blanca Formation of Colombia

Hybodonts are thought to have been generally relatively slow swimmers, though capable of fast bursts of locomotion. [30] Some hybodonts like Hybodus are thought to have been active predators capable of feeding on swiftly moving prey, [2] with preserved stomach contents of a specimen of Hybodus hauffianus indicating that they fed on belemnites (a type of extinct squid-like cephalopod). [31] Hybodonts have a wide variety of tooth shapes. This variety suggests that they took advantage of multiple food sources. [8] It is thought that some hybodonts which had wider, flatter, teeth specialized in crushing or grinding hard-shelled prey (durophagy), [20] with some hybodonts like Asteracanthus probably consuming both hard and soft bodied prey. [4] Often multiple species of hybodonts with different prey preferences coexisted within the same ecosystem. [32] [11]

Evolutionary history

Fossil of Hamiltonichthys a primitive hybodont from the Carboniferous of North America Hamiltonichthys mapesi.jpg
Fossil of Hamiltonichthys a primitive hybodont from the Carboniferous of North America

The earliest hybodont remains are from the latest Devonian (Famennian, ~ 360 million years ago) of Iran, belonging to the genus Roongodus, [33] as well as remains assigned to Lissodus of the same age from Belgium. [34] Carboniferous hybodonts include both durophagous and non-durophagous forms, while durophagous forms were dominant during the Permian period. [34] By the Permian period, hybodonts had a global distribution. [34] [35] [36] The Permian-Triassic extinction event only had a limited effect on hybodont diversity. [30] Maximum hybodont diversity is observed during the Triassic. During the Triassic and Early Jurassic, hybodontiforms were the dominant elasmobranchs in both marine and non-marine environments. [20] A shift in hybodonts was seen during the Middle Jurassic, a transition between the distinctly different assemblages seen in the Triassic – Early Jurassic and the Late Jurassic – Cretaceous. [20] As neoselachians (group of modern sharks) diversified further during the Late Jurassic, hybodontiforms became less prevalent in open marine conditions but remained diverse in fluvial and restricted settings during the Cretaceous. [20] Possible reasons for the replacement of hybodonts by modern sharks include more effective locomotory and jaw movement mechanisms of the latter group. [37] By the end of the Cretaceous, hybodonts had declined to only a handful of species, [38] including members of Lonchidion [39] , and Meristodonoides. [40] The last hybodonts disappeared, seemingly abruptly, as part of the Cretaceous-Paleogene extinction event approximately 66 million years ago. [38]

Families and genera

The taxonomy of hybodonts is considered poorly resolved, [4] so the classification presented should not be taken as authoritative.

Related Research Articles

<span class="mw-page-title-main">Elasmobranchii</span> Subclass of fishes

Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks, rays, skates, and sawfish. Members of this subclass are characterised by having five to seven pairs of gill slits opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.

<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.

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

Xenacanthida is an order or superorder of extinct shark-like chondrichthyans known from the Carboniferous to Triassic. They were native to freshwater, marginal marine and shallow marine habitats. Some xenacanths may have grown to lengths of 5 m (16 ft). Most xenacanths died out at the end of the Permian in the End-Permian Mass Extinction, with only a few forms surviving into the Triassic.

<i>Hybodus</i> Extinct genus of shark-like hybodont

Hybodus is an extinct genus of hybodont that lived from the Middle Triassic to the Late Cretaceous periods. Species closely related to the type species Hybodus reticulatus lived during the Early Jurassic epoch. Numerous species have been assigned to Hybodus spanning a large period of time, and it is currently considered a wastebasket taxon that is 'broadly polyphyletic' and requires reexamination.

<i>Lonchidion</i> Extinct genus of hybodont shark

Lonchidion is a genus of extinct hybodont in the family Lonchidiidae. The genus first appears in the fossil record during the Middle Triassic (Ladinian) and was among the last surviving hybodont genera, with its youngest known fossils dating to the very end of the Cretaceous (Maastrichtian).

<i>Palaeoxyris</i> Trace fossil

Palaeoxyris is a morphogenus of eggs cases, widely thought to have been produced by hybodonts, with a predominant occurrence in ancient freshwater environments. They comprise a beak, a body and a pedicle. They display a conspicuous right-handed spiral of collarettes around the body, and in some cases, the pedicle, resulting in a rhomboidal pattern when flattened during fossilisation. At the end of the beak was a tendril which attached the egg to vegetation during development. The body of the egg ranges in length from 1.2–8.9 centimetres (0.47–3.50 in), depending on the species.

<i>Meristodonoides</i> Extinct genus of hybodont chondrichthyans

Meristodonoides is an extinct genus of hybodont known from the mid-late Cretaceous, with potential records dating back to the Jurassic. It is one of a number of hybodont genera composed of species formerly assigned to Hybodus.

<i>Asteracanthus</i> Extinct genus of hybodonts

Asteracanthus is an extinct genus of hybodont, known from the Middle Jurassic (Bathonian) to the Early Cretaceous (Valanginian).

This list of fossil fishes described in 2017 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fishes, bony fishes and other fishes of every kind that are scheduled to be described during the year 2017, as well as other significant discoveries and events related to paleontology of fishes that are scheduled to occur in the year 2017. The list only includes taxa at the level of genus or species.

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

Synechodontiformes is an extinct order of prehistoric shark-like cartilaginous fish, known from the Permian to the Paleogene. They are considered to be members of Neoselachii, the group that contains modern sharks and rays.

This list of fossil fish described in 2018 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fish, bony fish, and other fish of every kind that are scheduled to be described during the year 2018, as well as other significant discoveries and events related to paleontology of fish that are scheduled to occur in 2018.

<i>Synechodus</i> Fossil genus of cartilaginous fish

Synechodus is an extinct genus of shark belonging to the family Palaeospinacidae and order Synechodontiformes. It is known from 16 species primarily spanning from the Late Triassic to Paleocene. The dentition is multicusped and was used for grasping. Several species are known from skeletal remains, including the species Synechodus ungeri from the Late Jurassic of Germany, which shows that it was relatively short with large pectoral fins and a proportionally large head with a round snout. This species is suggested to have reached a body length of 30–40 centimetres (0.98–1.31 ft). Skeletal remains are also known of the species Synechodus dubrisiensis from the Cretaceous of Europe. A skeleton of an indeterminate species is also known from the Early Cretaceous (Albian) of France, with a body length of around 70 centimetres (2.3 ft). Synechodus is suggested to have had two dorsal fins that lacked fin spines, though the number of dorsal fins is unknown in Synechodus ungeri.

Tribodus is an extinct genus of hybodont. It lived during the mid Cretaceous (Albian-Cenomanian) with fossils being known from northern South America, North Africa, and southern Europe.

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

Ctenacanthiformes is an extinct order of cartilaginous fish. They possessed ornamented fin spines at the front of their dorsal fins and cladodont-type dentition, that is typically of a grasping morphology, though some taxa developed cutting and gouging tooth morphologies. Some ctenacanths are thought to have reached sizes comparable to the great white shark, with body lengths of up to 7 metres (23 ft) and weights of 1,500–2,500 kilograms (3,300–5,500 lb), while others reached lengths of only 30 centimetres (12 in). The earliest ctenacanths appeared during the Frasnian stage of the Late Devonian, with the group reaching their greatest diversity during the Early Carboniferous (Mississippian), and continued to exist into at least the Middle Permian (Guadalupian). Some authors have suggested members of the family Ctenacanthidae may have survived into the Cretaceous based on teeth found in deep water deposits of Valanginian age in France and Austria, however, other authors contend that the similarity of these teeth to Paleozoic ctenacanths is only superficial, and they likely belong to neoselachians instead.

This list of fossil fish research presented in 2021 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fishes, bony fishes, and other fishes that were described during the year, as well as other significant discoveries and events related to paleoichthyology that occurred in 2021.

<i>Strophodus</i> Extinct genus of fishes

Strophodus is an extinct genus of durophagous hybodont known from the Triassic to Cretaceous. It was formerly confused with Asteracanthus.

This list of fossil fish research presented in 2023 is a list of new fossil taxa of jawless vertebrates, placoderms, cartilaginous fishes, bony fishes, and other fishes that were described during the year, as well as other significant discoveries and events related to paleoichthyology that occurred in 2023.

<i>Egertonodus</i> Extinct genus of shark-like fish

Egertonodus is an extinct genus of shark-like hybodont fish. It includes E. basanus from the Jurassic of Europe and North Africa and Cretaceous of North America, North Africa and Europe, and E. duffini from the Middle Jurassic of England. Indeterminate remains of the genus have been reported from the Early Cretaceous of Asia. E. basanus is known from preserved skull material, while E. duffini is only known from teeth. The genus is distinguished from Hybodussensu stricto by characters of the skull and teeth. E. basanus, the most common species, is thought to have reached 1.5 m in length. E. fraasi from the Late Jurassic of Germany, known from a poorly preserved full body fossil, was placed in Egertonodus in one study, but this has been subsequently questioned by other authors, due to strong differences in tooth morphology from the type species. Fossils have been found in freshwater and lagoonal environments.

<i>Planohybodus</i> Genus of hybodont

Planohybodus is an extinct genus of hybodont, known from the Middle Jurassic-Early Cretaceous (Bathonian-Barremian) of Europe and the Indian subcontinent. Fossils have been found in marine as well as freshwater environments. The genus contains 3 confirmed species, two of which were originally assigned to the genus Hybodus. Possible records have been reported from the Late Jurassic of Mexico, the Early Cretaceous of Brazil and the Late Cretaceous (Santonian) of North America, but these are unconfirmed. Planohybodus peterboroughensis is suggested to have reached lengths of 2–3 metres (6.6–9.8 ft). A specimen of the ammonite genus Orthaspidoceras from the Late Jurassic of France has been found with an embedded tooth of Planohybodus, suggesting that while the teeth of Planohybodus were adapted to tearing soft bodied prey, it would attack hard-shelled prey at least on occasion.

This list of fossil fish research presented in 2024 is a list of new fossil taxa of jawless vertebrates, placoderms, cartilaginous fishes, bony fishes, and other fishes that were described during the year, as well as other significant discoveries and events related to paleoichthyology that occurred in 2024.

References

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  18. ↑ Maisey, John G.; Denton, John S. S. (2016-09-02). "Dermal denticle patterning in the Cretaceous hybodont shark Tribodus limae (Euselachii, Hybodontiformes), and its implications for the evolution of patterning in the chondrichthyan dermal skeleton". Journal of Vertebrate Paleontology. 36 (5): e1179200. Bibcode:2016JVPal..36E9200M. doi: 10.1080/02724634.2016.1179200 . ISSN   0272-4634. S2CID   88591830.
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  22. ↑ Wen, Wen; Kriwet, JüRgen; Zhang, Qiyue; Benton, Michael J.; Duffin, Christopher J.; Huang, Jingyuan; Zhou, Changyong; Hu, Shixue; Ma, Zhixin (2022-06-30). "Hybodontiform shark remains (Chondrichthyes, Elasmobranchii) from the Lower Triassic of Yunnan Province, China, with comments on hybodontiform diversity across the PTB". Journal of Vertebrate Paleontology. 42 (1). Bibcode:2022JVPal..42E8712W. doi:10.1080/02724634.2022.2108712. ISSN   0272-4634. S2CID   252136919.
  23. ↑ Fischer, Jan; Schneider, Jörg W.; Voigt, Silke; Joachimski, Michael M.; Tichomirowa, Marion; Tütken, Thomas; Götze, Jens; Berner, Ulrich (2013-03-29). "Oxygen and strontium isotopes from fossil shark teeth: Environmental and ecological implications for Late Palaeozoic European basins". Chemical Geology. 342: 44–62. Bibcode:2013ChGeo.342...44F. doi:10.1016/j.chemgeo.2013.01.022. ISSN   0009-2541.
  24. ↑ Klug, Stefanie; Tütken, Thomas; Wings, Oliver; Pfretzschner, Hans-Ulrich; Martin, Thomas (2010-09-01). "A Late Jurassic freshwater shark assemblage (Chondrichthyes, Hybodontiformes) from the southern Junggar Basin, Xinjiang, Northwest China". Palaeobiodiversity and Palaeoenvironments. 90 (3): 241–257. Bibcode:2010PdPe...90..241K. doi:10.1007/s12549-010-0032-2. ISSN   1867-1608. S2CID   129236098.
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  27. ↑ Turmine-Juhel, Pernelle; Wilks, Richard; Brockhurst, David; Austen, Peter A.; Duffin, Christopher J.; Benton, Michael J. (December 2019). "Microvertebrates from the Wadhurst Clay Formation (Lower Cretaceous) of Ashdown Brickworks, East Sussex, UK". Proceedings of the Geologists' Association. 130 (6): 752–769. Bibcode:2019PrGA..130..752T. doi:10.1016/j.pgeola.2019.08.003. S2CID   202904040.
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