Hyperkynodon
Encyclopedia
Hyperokynodon is an extinct genus
of trematosauria
n temnospondyl within the family
Trematosauridae
. Fossils have been found in Germany
. While most trematosaurids existed during the Early Triassic
, Hyperokynodon has been found in Late Triassic
deposits, making it the youngest known trematosaurid. Hyperokyodon was known since 1852, but it was not identified as a trematosaurid until 1987. The type
and only species is H. keuperinus.
snout and a cast of the underside of the skull roof
. The holotype was found in Heilbronn
, 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
quarry east of the city of Heilbronn
. SMNS 55910 is an impression of the underside of the skull table and includes parts of the palate
and the edge of the orbit
.
Based on the cast, the total skull length is estimated to have been around 80 centimetres (31.5 in). The total body length based on related trematosaurs is estimated to have been 2.8 metres (9.2 ft) to 3.2 metres (10.5 ft). Like other trematosaurids, Hyperokynodon has a narrow skull. The back portion, however, is unusually narrow, approaching that of Cosgriffius, 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
, such as the absence of teeth between the choana
e.
for many decades. In 1987, it was given a more specific classification as a tertremine trematosaurid.
German paleontologist Eberhard Fraas
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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of trematosauria
Trematosauria
Trematosauria is one of two major groups of temnospondyl amphibians that survived the Permian-Triassic extinction event, the other being the Capitosauria. The trematosaurs were a diverse and important group that included many medium-sized to large forms that were semi-aquatic to totally aquatic...
n temnospondyl within the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Trematosauridae
Trematosauridae
Trematosauridae are a family of large temnospondyl amphibians with many members. They first appeared during the Olenekian stage of the Early Triassic, and existed up until around the Carnian stage of the Late Triassic, although by then they were very rare...
. Fossils have been found in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. While most trematosaurids existed during the Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
, Hyperokynodon has been found in Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
deposits, making it the youngest known trematosaurid. Hyperokyodon was known since 1852, but it was not identified as a trematosaurid until 1987. The type
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
and only species is H. keuperinus.
Description
Hyperokynodon is known only from two specimens: a holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
snout and a cast of the underside of the skull roof
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, hence the alternative name dermatocranium...
. The holotype was found in Heilbronn
Heilbronn (district)
Heilbronn is a district in the north of Baden-Württemberg, Germany. Neighboring districts are Neckar-Odenwald, Hohenlohe, Schwäbisch Hall, Rems-Murr, Ludwigsburg, Enz, Karlsruhe and Rhein-Neckar...
, Germany, in the mid-1800s. It likely came from deposits in the Wartberg
Wartberg (Heilbronn)
Wartberg is a mountain of Baden-Württemberg, Germany....
, a mountain that had several active quarries at the time. The cast, known as SMNS 55910, was found in a sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
quarry east of the city of Heilbronn
Heilbronn
Heilbronn is a city in northern Baden-Württemberg, Germany. It is completely surrounded by Heilbronn County and with approximately 123.000 residents, it is the sixth-largest city in the state....
. SMNS 55910 is an impression of the underside of the skull table and includes parts of the palate
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 separate. The palate is divided into two parts, the anterior...
and the edge of the orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
.
Based on the cast, the total skull length is estimated to have been around 80 centimetres (31.5 in). The total body length based on related trematosaurs is estimated to have been 2.8 metres (9.2 ft) to 3.2 metres (10.5 ft). Like other trematosaurids, Hyperokynodon has a narrow skull. The back portion, however, is unusually narrow, approaching that of Cosgriffius, a lonchorhynchine
Lonchorhynchinae
Lonchorhynchinae is a subfamily of temnospondyl amphibians within the family Trematosauridae.-External links:*...
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
Tertrema is an extinct genus of trematosaurian temnospondyl within the family Trematosauridae.-See also:* Prehistoric amphibian* List of prehistoric amphibians...
, such as the absence of teeth between the choana
Choana
Choana is the posterior nasal aperture.The choanae are separated by the vomer.- Boundaries :It is the opening between the nasal cavity and the nasopharynx....
e.
Classification
The fragmentary nature of specimens belonging to Hyperokynodon has led to difficulty in classification. The genus was placed in the capitosaur family MastodonsauroideaMastodonsauroidea
The Mastodonsauroidea are an extinct superfamily of temnospondyl amphibians known from the Triassic and Jurassic. Fossils belonging to this superfamily have been found in North America, Greenland, Europe, Asia, and Australia...
for many decades. In 1987, it was given a more specific classification as a tertremine trematosaurid.
German paleontologist Eberhard Fraas
Eberhard Fraas
Eberhard Fraas was a German geologist and paleontologist. He worked as a curator at the Stuttgarter Naturaliensammlung and discovered the dinosaurs of the Tendaguru formation in then German East Africa ....
referred SMNS 55910 to the metoposaur
Metoposauridae
Metoposauridae is an extinct family of trematosaurian temnospondyls. The family is known from the Triassic and Jurassic periods. Most members are large, approximately long...
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.
See also
- Prehistoric amphibian
- List of prehistoric amphibians