''Hyperokynodon'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

trematosauria Trematosauria is one of two major groups of temnospondyl amphibians that survived the Permian-Triassic extinction event, the other (according to Yates and Warren 2000) being the Capitosauria. The trematosaurs were a diverse and important group th ...

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...

within the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Trematosauridae Trematosauridae are a family of large marine temnospondyl amphibians with many members. They first appeared during the Induan age of the Early Triassic, and existed until around the Carnian stage of the Late Triassic, although by then they wer ...

. Fossils have been found in

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

. While most trematosaurids existed during the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

, ''Hyperokynodon'' has been found in

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

deposits, making it the youngest known trematosaurid. ''Hyperokynodon'' was known since 1852, but it was not identified as a trematosaurid until 1987. The type and only species is ''H. keuperinus''.

Description

''Hyperokynodon'' is known only from two specimens: a

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

snout and a cast of the underside of the

skull roof The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In comparati ...

. The holotype was found in

Heilbronn Heilbronn () is a List of cities and towns in Germany, city in northern Baden-Württemberg, Germany, surrounded by Heilbronn (district), Heilbronn District. With over 126,000 residents, it is the sixth-largest city in the state. From the late Mid ...

, Germany, in the mid-1800s. It likely came from deposits in the Wartberg, a mountain that had several active quarries at the time. The cast, known as SMNS 55910, was found in a

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

quarry east of the city of

. SMNS 55910 is an impression of the underside of the skull table and includes parts of the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...

and the edge of the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

. Based on the cast, the total skull length is estimated to have been around . The total body length based on related trematosaurs is estimated to have been to . Like other trematosaurids, ''Hyperokynodon'' has a narrow skull. The back portion, however, is unusually narrow, approaching that of ''

Cosgriffius ''Cosgriffius'' is an extinct genus of trematosaurian temnospondyl within the family Trematosauridae. It was described in 1993 by Samuel P. Welles based on a single partial skull from the well-known Meteor Crater Quarry (Early Triassic Moenkopi F ...

'', a lonchorhynchine 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 ''Tertrema'' is an extinct genus of trematosaurian temnospondyl within the family Trematosauridae. It has an elongate snout and widely spaced occipital condyles. See also * Prehistoric amphibian * List of prehistoric amphibians This list of pre ...

'', such as the absence of teeth between the

choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...

Classification

The fragmentary nature of specimens belonging to ''Hyperokynodon'' has led to difficulty in classification. The genus was placed in the

capitosaur Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts t ...

family

Mastodonsauroidea The Mastodonsauroidea are an extinct superfamily of temnospondyl amphibians known from the Triassic. Fossils belonging to this superfamily have been found in North America, Greenland, Europe, Asia, and Australia. The genus '' Ferganobatrachus'' ...

for many decades. In 1987, it was given a more specific classification as a tertremine trematosaurid. German

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Eberhard Fraas Eberhard Fraas (26 June 1862 – 6 March 1915) was a German scientist, geologist and paleontologist. He worked as a curator at the Stuttgarter Naturaliensammlung and discovered the dinosaurs of the Tendaguru formation in then German East Afric ...

referred SMNS 55910 to the metoposaur ''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.

References

{{Taxonbar, from=Q5958370 Trematosaurs Fossils of Germany Triassic temnospondyls of Europe Fossil taxa described in 1852