''Hybodus'' (from el, ύβος , 'crooked' and el, ὀδούς 'tooth') is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial no ...

hybodont Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like chondrichthyans, which existed from the late Devonian to the Late Cretaceous. They form the group of Elasmobranchii closest to neoselachians, the clade of modern sha ...

, a group of

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...

-like elasmobranchs that lived from the Late

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

to the end of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

. Species closely related to the type species ''Hybodus reticulatus'' lived during the

Early Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma&nb ...

epoch. Numerous species have been assigned to ''Hybodus'' spanning a large period of time, and it is currently considered a

wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically defined ...

that is 'broadly

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

' and requires reexamination. The first fossilized teeth from ''Hybodus'' were found in England around 1845; since then teeth (and dorsal spines) have been recovered from Europe. During the Triassic, Jurassic, and Cretaceous periods, the hybodonts were especially successful and could be found in shallow seas around the world. For reasons that are not fully understood, the hybodonts became extinct near the end of the Late Cretaceous period.

Description

''Hybodus'' species grew to about in length. It was not very big, but had the classic streamlined shark shape, complete with two

dorsal fins A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

that would have helped it steer with precision. As in other Hybodontiformes, dentinous fin spines were present on the dorsal fins of ''Hybodus''. The fin spines of ''Hybodus'' exhibit a rib-like ornamentation located towards the tip of the spine, with rows of hooked denticles present on the posterior side. The spines may have played a role in defending the animal from predators. ''Hybodus varied dentition would have allowed it to opportunistically exploit a variety of food sources; sharper teeth would have been used to catch slippery prey, while the flatter teeth probably helped them crush shelled creatures. The males also possessed

clasper In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's ...

s, specialized organs that directly insert sperm into the female, and which are still present in modern sharks.

Species

Several ''Hybodus'' species, including ''H. butleri'', ''H. rajkovichi'', and ''H. montanensis'', were later reassigned to '' Meristodonoides''. ''H. basanus'' and ''H. fraasi'' is now included in the genus '' Egertonodus''. ''H. obtusus'' represents a junior synonym of '' Asteracanthus ornatissimus''. A new species from Spain, ''H. bugarensis'', is described in 2013. Two new species from China, ''H. xinzhuangensis'' and ''H. chuanjieensis'' are named in 2018, and ''H. houtienensis'' is considered, while other species from China and Thailand are no longer part of the genus and requires reassessment. However, the only two species that should be retained within the genus ''Hybodus'' are the type species ''H. reticulatus'' and the other species ''H. hauffianus''. The problem is that even those two species require reassessment.Stumpf, S., & Kriwet, J. (2019). A new Pliensbachian elasmobranch (Vertebrata, Chondrichthyes) assemblage from Europe, and its contribution to the understanding of late Early Jurassic elasmobranch diversity and distributional patterns. ''PalZ, 93''(4), 637–658. https://doi.org/10.1007/s12542-019-00451-4

References

Sources

* * Hybodontiformes Prehistoric shark genera Permian sharks Triassic sharks Jurassic sharks Cretaceous sharks Prehistoric fish of Africa Cretaceous fish of Asia Fossils of Uzbekistan Bissekty Formation Prehistoric fish of Europe Hasle Formation Prehistoric fish of South America Taxa named by Louis Agassiz {{Jurassic-fish-stub