Synechodontiformes

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Synechodontiformes
Temporal range: Early Permian-Paleogene 290.1–37.2  Ma [1]
Synechodus.png
Fossil of Synechodus ungeri from the Late Jurassic of Germany
Rya Formation shark teeth - Synechodus - S. occultidens (A-G) & S. enniskilleni (H-J).jpg
Fossil teeth of Palidiplospinax occultidens (top) and P. enniskilleni
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Clade: Neoselachii
Order: Synechodontiformes
Duffin & Ward, 1993 [2]
Families

See text

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.

Contents

Their placement in the group is uncertain, some authors have considered them to be members of the modern shark group Galeomorphii, while others have considered them to represent a stem-group to modern sharks, [3] [4] with some suggesting that they are basal to the last common ancestor of modern sharks and rays. [5] There is also disagreement about the relationships between Triassic and earlier members of the group, only known from isolated teeth, and those from the Jurassic onwards, with the similarity between the two groups possibly being superficial. [6]

The main shared characters of the group relate to teeth anatomy. The teeth roots have a distinctive pseudopolyaulacorhize vascularisation pattern, with a depression on the tooth root to where the nutritive grooves are confined. While Klug (2010) recovered the group as monophyletic, [4] the monophyly of the group has been doubted by other authors, who suggest that they represent a paraphyletic group. [5] One family is unambiguously placed in the order, Palaeospinacidae. The families Orthacodontidae, Paraorthacodontidae and Pseudonotidanidae, often considered members of the group, have been alternatively considered as members of the modern shark order Hexanchiformes rather than as members of Synechodontiformes. [7]

The oldest known synechodontiform remains are teeth of Synechodus antiquus from the early Permian (Cisuralian) of the Ural Mountains. [8] However, other authors have considered the attribution to the teeth to Synechodus to be questionable. [6]

Taxonomy

Disputed members

These members were classified in the Synechodontiformes by Klug (2010), but are classified by some other authors as Hexanchiformes: [10] [18] [7]

Related Research Articles

<span class="mw-page-title-main">Hexanchiformes</span> Order of sharks

The Hexanchiformes are a primitive order of sharks, that numbering just seven extant species in two families. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens.

<span class="mw-page-title-main">Lamniformes</span> Order of sharks

The Lamniformes are an order of sharks commonly known as mackerel sharks. It includes some of the most familiar species of sharks, such as the great white, as well as more unusual representatives, such as the goblin shark and megamouth shark.

<span class="mw-page-title-main">Cow shark</span> Family of sharks

Cow sharks are a shark family, the Hexanchidae, characterized by an additional pair or pairs of gill slits. Its 37 species are placed within the 10 genera: Gladioserratus, Heptranchias, Hexanchus, Notidanodon, Notorynchus, Pachyhexanchus, Paraheptranchias, Pseudonotidanus, Welcommia, and Weltonia.

<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 clefts 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.

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

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, a group of shark-like euselachians that lived from the Late Devonian to the end of the Cretaceous. 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.

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

Symmoriiformes is an extinct order of stem-group holocephalians. Originally named Symmoriida by Zangerl (1981), it has subsequently been known by several other names. Lund (1986) synonymized the group with Cladodontida, while Maisey (2008) corrected the name to Symmoriiformes in order to prevent it from being mistaken for a family. The symmoriiform fossils record begins during the late Devonian. Most of them died out at the start of the Permian, but Dwykaselachus is known from the Artinskian-Kungurian of South Africa. Teeth described from the Valanginian of France and Austria indicate that members of the family Falcatidae might have survived until the Early Cretaceous; however, these teeth were also argued to be more likely neoselachian teeth.

<span class="mw-page-title-main">Hybodontiformes</span> Extinct order of chondrichthyans

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.

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

Paraorthacodus is an extinct genus of shark. It a member of the family Paraorthacodontidae, which is either placed in Hexanchiformes or in Synechodontiformes. It is known from 11 species spanning from the Early Jurassic to the Eocene. Full body fossils from the Late Jurassic of Germany suggest that juveniles had a robust body with a round head, while adults had large body sizes with a fusiform profile. There was only a single dorsal fin towards the back of the body without a fin spine. The dentition had teeth with a single large central cusp along with shorter lateral cusplets, which where designed for clutching.

Meristodonoides is an extinct genus of hybodont. The type species is M. rajkovichi, which was originally a species in the genus Hybodus. The species, along with other Hybodus species such as H. butleri and H. montanensis, was reassigned to Meristodonoides by Charlie J. Underwood and Stephen L. Cumbaa in 2010. The species is primarily known from remains from the Cretaceous of North America, spanning from the Aptian/Albian to Maastrichtian, making it one of the last surviving hybodont genera, though records of the genus likely extend back as far as the Late Jurassic, based on an undescribed skeleton from the Tithonian of England, and fragmentary teeth from the Kimmeridgian of Poland, England and Switzerland. Other remains of the genus are known from the Coniacian of England, the Aptian-Albian of France, and the Campanian of European Russia. The morphology of the teeth suggests an adaptation to tearing prey. Fossils from the Western Interior Seaway suggest that it preferred nearshore marine environments, being absent from deeper-water areas, with it likely also being able to tolerate brackish and freshwater conditions.

Palaeospinax is an extinct genus of synechodontiform cartilaginous fish. Although several species have been described, the genus is considered nomen dubium because the type-specimen of the type species, Palaeospinax priscus, from the Late Triassic-Early Jurassic of Europe lacks appropriate diagnostic characters to define the genus.

This list of fossil fishes described in 2014 is a list of new taxa of placoderms, fossil cartilaginous fishes and bony fishess of every kind that have been described during the year 2014, as well as other significant discoveries and events related to paleontology of fishes that occurred in the year 2014. The list only includes taxa at the level of genus or species.

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

Mcmurdodus is an extinct genus of chondrichthyan from Antarctica and Australia and the sole member of the family Mcmurdodontidae. It contains two extinct species. However, the Australian species M. whitei has been found to be different from the Antarctic type species M. featherensis, and thus M. whitei has been classified into a new genus, Maiseyodus.

<span class="mw-page-title-main">Cladodont</span> Early Devonian shark tooth structure

Cladodont is the term for a common category of early Devonian shark known primarily for its "multi-cusped" tooth consisting of one long blade surrounded by many short, fork-like tines, designed to catch food that was swallowed whole, instead of being used to saw off chunks of meat like many modern sharks. The skinny teeth would puncture and grasp the prey, keeping it from wriggling free.

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

Paracestracion is an extinct genus of heterodontiform sharks from Early Jurassic to Early Cretaceous-aged rocks of England, France, Germany and Luxembourg. The genu was first described in 1911 by Ernst Hermann Friedrich von Koken in Karl Alfred von Zittel.

<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.

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

Pseudorhina is an extinct genus of stem angel shark seemingly restricted to the Mesozoic of Europe. It is represented by several articulated individuals as well as isolated teeth. There are currently four species.

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

Ctenacanthiformes is an extinct order of elasmobranch 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). Ctenacanths are typically thought to have existed from the Devonian to the Late Permian, becoming extinct in the Permian-Triassic extinction event. 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. The monophyly of the group has been questioned, with some studies recovering the group as a whole as paraphyletic or polyphyletic.

This list of fossil fish research presented in 2023 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 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.

References

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