# Hyperokynodon

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Extinct genus of amphibians

Hyperokynodon Temporal range: Carnian Scientific classification Kingdom: Animalia Phylum: Chordata Clade: Tetrapoda Order: †Temnospondyli Suborder: †Stereospondyli Family: †Trematosauridae Genus: †Hyperokynodon Plieninger, 1852 Species H. keuperinus Plieninger, 1852 (type)

***Hyperokynodon*** is an extinct [genus](/source/Genus) of [trematosaurian](/source/Trematosauria) [temnospondyl](/source/Temnospondyl) within the [family](/source/Family_(taxonomy)) [Trematosauridae](/source/Trematosauridae). Fossils have been found in [Germany](/source/Germany). While most trematosaurids existed during the [Early Triassic](/source/Early_Triassic), *Hyperokynodon* has been found in [Late Triassic](/source/Late_Triassic) deposits, making it the youngest known trematosaurid. *Hyperokynodon* was known since 1852, but it was not identified as a trematosaurid until 1987. The [type](/source/Type_species) and only species is *H. keuperinus*.

## Description

*Hyperokynodon* is known only from two specimens: a [holotype](/source/Holotype) snout and a cast of the underside of the [skull roof](/source/Skull_roof). The holotype was found in [Heilbronn](/source/Heilbronn_(district)), Germany, in the mid-1800s. It likely came from deposits in the [Wartberg](/source/Wartberg_(Heilbronn)), a mountain that had several active quarries at the time. The cast, known as SMNS 55910, was found in a [sandstone](/source/Sandstone) quarry east of the city of [Heilbronn](/source/Heilbronn). SMNS 55910 is an impression of the underside of the skull table and includes parts of the [palate](/source/Palate) and the edge of the [orbit](/source/Orbit_(anatomy)).[1]

Based on the cast, the total skull length is estimated to have been around 80 centimetres (31 in). The total body length based on related trematosaurs is estimated to have been 2.8 metres (9.2 ft) to 3.2 metres (10 ft). Like other trematosaurids, *Hyperokynodon* has a narrow skull. The back portion, however, is unusually narrow, approaching that of *[Cosgriffius](/source/Cosgriffius)*, a [lonchorhynchine](/source/Lonchorhynchinae) trematosaurid with a very narrow skull. The snout is moderately elongated with a wide tip. The anterior palatal openings, two holes at the front of the palate, are widely spaced. The vomerine and palatal fangs, two sets of teeth on the roof of the mouth, are very large and laterally compressed. *Hyperokynodon* shares several characteristics with the related *[Tertrema](/source/Tertrema)*, such as the absence of teeth between the [choanae](/source/Choana).[1]

## Classification

The fragmentary nature of specimens belonging to *Hyperokynodon* has led to difficulty in classification.[2] The genus was placed in the [capitosaur](/source/Capitosaur) family [Mastodonsauroidea](/source/Mastodonsauroidea) for many decades.[3] In 1987, it was given a more specific classification as a [tertremine](https://en.wikipedia.org/w/index.php?title=Tertreminae&action=edit&redlink=1) trematosaurid.[4]

German [paleontologist](/source/Paleontologist) [Eberhard Fraas](/source/Eberhard_Fraas) referred SMNS 55910 to the [metoposaur](/source/Metoposauridae) *Metopias* in 1889. Schoch *et al.* (2002) considered the cast to belong to *H. keuperinus* because it was the only other trematosaurid known from Heilbronn. Schoch *et al.* also raised the possibility that it was a lonchorhynchine, which would imply that both the lonchorhynchine and tertremine lineages survived into the Late Triassic. Schoch *et al.* considered the cast to belong to a tertremine, however, because of its large size and distinctive features.[1]

## See also

- [Paleontology portal](https://en.wikipedia.org/wiki/Portal:Paleontology)

- [List of prehistoric amphibians](/source/List_of_prehistoric_amphibians)

## References

1. ^ [***a***](#cite_ref-SMH02_1-0) [***b***](#cite_ref-SMH02_1-1) [***c***](#cite_ref-SMH02_1-2) Schoch, R.R.; Milner, A.R.; Hellrung, H. (2002). ["The last trematosaurid amphibian *Hyperokynodon keuperinus* revisited"](http://www-alt.naturkundemuseum-bw.de/stuttgart/pdf/b_pdf/B321.pdf) (PDF). *Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie)*. **321**: 1–9. [ISSN](/source/ISSN_(identifier)) [0341-0153](https://search.worldcat.org/issn/0341-0153).

1. **[^](#cite_ref-WB85_2-0)** Warren, A.; Black, T. (1985). "A new rhytidosteid (Amphibia, Labyrinthodontia) from the Early Triassic Arcadia Formation of Queensland, Australia, and the relationships of Triassic temnospondyls". *Journal of Vertebrate Paleontology*. **5** (4): 303–327. [doi](/source/Doi_(identifier)):[10.1080/02724634.1985.10011868](https://doi.org/10.1080%2F02724634.1985.10011868).

1. **[^](#cite_ref-CEC46_3-0)** Case, E.C. (1946). "A census of the determinable genera of the Stegocephalia". *Transactions of the American Philosophical Society*. **35** (4): 323–420. [doi](/source/Doi_(identifier)):[10.2307/1005567](https://doi.org/10.2307%2F1005567). [hdl](/source/Hdl_(identifier)):[2027/mdp.39015071637537](https://hdl.handle.net/2027%2Fmdp.39015071637537).

1. **[^](#cite_ref-HH87_4-0)** Hellrung, H. (1987). "Revision von *Hyperokynodon keuperinus* Plieninger (Amphibia: Temnospondyli) aus dem Schilfsandstein von Heilbronn (Baden-Württemberg)". *Stuttgarter Beiträge zur Naturkunde*. **136**: 1–28.

v t e Stereospondyli Kingdom: Animalia Phylum: Chordata Clade: Tetrapodomorpha Order: Temnospondyli Tetrapodomorpha see Tetrapodomorpha Temnospondyli see Temnospondyli Stereospondyli see below↓ Stereospondyli Stereospondyli Arachana Capulomala Peltobatrachus Lapillopsidae Lapillopsis Manubrantlia Rhigerpeton Rotaurisaurus Rhinesuchidae Australerpeton? Broomistega Laccosaurus Parapytanga? Rastosuchus Rhineceps Rhinesuchoides Rhinesuchus Uranocentrodon Lydekkerinidae Chomatobatrachus Cryobatrachus Deltacephalus Eolydekkerina Indobenthosuchus Luzocephalus? Lydekkerina Capitosauria Antarctosuchus Bukobaja Calmasuchus Capitosaurus Cherninia Cyclotosaurus Edingerella Eocyclotosaurus Eryosuchus Heptasaurus Huangfuchuansuchus Jammerbergia Kestrosaurus Kupferzellia Mastodonsaurus Meyerosuchus Odenwaldia Paracyclotosaurus Parotosuchus Quasicyclotosaurus Procyclotosaurus Promastodonsaurus Rhadalognathus Samarabatrachus Sassenisaurus Sclerothorax Selenocara Stanocephalosaurus Stenotosaurus Subcyclotosaurus Tatrasuchus Vladlenosaurus Volgasaurus Volgasuchus Warrenisuchus Watsonisuchus Wellesaurus Wetlugasaurus Xenotosuchus Yuanansuchus Trematosauria see below↓ Trematosauria Trematosauria Almasaurus Bothriceps Callistomordax Chinlestegophis Keratobrachyops Laidleria Latiscopus Qantas Rileymillerus Syrtosuchus Uruyiella Benthosuchidae Benthosuchus Kwatisuchus Trematosauridae Angusaurus Aphaneramma Cosgriffius Erythrobatrachus Gonioglyptus Hyperokynodon Icanosaurus Indolyrocephalus Inflectosaurus Lyrocephaliscus Microposaurus Panchetosaurus Platystega Prothoosuchus Stoschiosaurus Tertrema Tertremoides Thoosuchus Tirraturhinus Trematolestes Trematosuchoides Trematosaurus Trematosuchus Trematotegmen Wantzosaurus Metoposauridae Anaschisma Apachesaurus Arganasaurus Buettnererpeton Dutuitosaurus Metoposaurus Panthasaurus Rhytidosteidae Boreopelta Mahavisaurus Nanolania Peltostega Pneumatostega Rhytidosteus Sangaia Trucheosaurus Derwentiinae Arcadia Acerastia Deltasaurus Derwentia Indobrachyops Rewana Chigutisauridae Arenaerpeton Chigutisaurus Compsocerops Koolasuchus Pelorocephalus Siderops Brachyopidae Banksiops Bathignathus Batrachosaurus Batrachosuchoides Batrachosuchus Blinasaurus Brachyops Gobiops Hadrokkosaurus Notobrachyops Platycepsion Sinobrachyops Vanastega Vigilius Xenobrachyops Plagiosauridae Gerrothorax Megalophthalma Plagiobatrachus Plagiorophus Plagiosaurus Plagioscutum Plagiosternum Plagiosuchus See also: Trematosauroidea Metoposauroidea Rhytidosteoidea Brachyopomorpha Brachyopoidea Plagiosauroidea Category

Taxon identifiers Hyperokynodon Wikidata: Q5958370 GBIF: 8492795 Open Tree of Life: 6159417 Paleobiology Database: 180128

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Adapted from the Wikipedia article [Hyperokynodon](https://en.wikipedia.org/wiki/Hyperokynodon) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Hyperokynodon?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.