Trematosaurus
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''Trematosaurus'' 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 nom ...
of
trematosaurid 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 ...
temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carbo ...
amphibian 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 ...
and
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
. It was first named by Hermann Burmeister in 1849 and the type species is ''Trematosaurus brauni''.


History of study

''Trematosaurus'' was one of the first temnospondyls to be described. The type locality, called Merkel's Quarry, is in east-central
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 ...
at Bernburg an der Saale within the Bausandstein (
Olenekian In the geologic timescale, the Olenekian is an age in the Early Triassic epoch; in chronostratigraphy, it is a stage in the Lower Triassic series. It spans the time between Ma and Ma (million years ago). The Olenekian is sometimes divided i ...
) and was collected for several decades from the 1840s into the early 20th century, producing extensive cranial remains, although the majority of these are preserved as internal molds (steinkerns) or natural molds. The name ''Trematosaurus'' was in fact coined in 1842 by Carl von Braun, a frequent collector who used the Greek suffix ''trema'' ('hole') in reference to the
pineal foramen A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhyth ...
to form the generic epithet, but as he provided no formal description, the name was not considered valid until the work of Burmeister, who named the type species after Braun. Burmeister's work was largely reconstructive and frequently omitted references to which specimens were being described, and as a result, it remains unknown which specimens exactly were covered in his description. This was remedied by subsequent workers who provided specimen illustrations for material reposited at numerous museums across Europe. However, the complete osteology and ontogeny of this taxon remained poorly documented until the work of Schoch (2019). Two other species were described from equivalent horizons in
Thuringia Thuringia (; german: Thüringen ), officially the Free State of Thuringia ( ), is a state of central Germany, covering , the sixth smallest of the sixteen German states. It has a population of about 2.1 million. Erfurt is the capital and lar ...
, ''T. fuchsi'' and ''T. thuringiensis''. ''Trematosaurus fuchsi'' is widely regarded as a junior synonym of ''T. brauni,'' while ''T. thuringiensis'' is tentatively considered to be valid with the caveat that poor preservation of the single specimen may account for some of the purported differences. ''Trematosaurus madagascariensis'' was synonymized with '' Tertremoides ambilobensis'' from the same horizon in
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
by Schoch & Milner (2000), with the species epithet of the former (named first) taking precedence by priority and the genus epithet of the latter taking precedence by distinction from ''Trematosaurus''. ''Trematosaurus sobeyi'' from
Cynognathus Assemblage Zone The ''Cynognathus'' Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossilife ...
of
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
was placed in the novel genus ''
Trematosuchus ''Trematosuchus'' is an extinct genus of trematosaurian temnospondyl within the family Trematosauridae from South Africa. It was first named by Haughton in 1915 as '' Trematosaurus sobeyi''. It was assigned to its own genus ''Trematosuchus'' by ...
'' by Watson (1919). ''Trematosaurus kannemeyeri'' from the same zone is thought to belong to '' Aphaneramma'', but other workers do not consider it to be diagnostic and thus to be invalid. ''Trematosaurus yakovlevi'' from Russia was placed in the novel genus '' Thoosuchus'' by Efremov (1940). ''Trematosaurus weidenbaumi'' was first removed to ''Thoosuchus'' and then placed in the novel genus '' Angusaurus'' by Getmanov (1989). Various reports of ''Trematosaurus'' sp. from
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
belong to '' Inflectosaurus'', but ''Trematosaurus galae'' is a recently described Russian species that remains valid to date.


Description

The overwhelming majority of specimens of ''T. brauni'' are partial to complete skulls, with 75 such specimens known (size range from 10.9 to 41 cm in length). Postcrania are restricted to the clavicle and interclavicle, two large plate-like elements of the pectoral girdle. In part, this relates to the occurrence of other large
stereospondyls The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecologi ...
at the type locality such as 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 labyrinthodont ...
'' Parotosuchus nasutus'', but postcrania are generally scarce, which may be due to either collection bias or taphonomic bias. Therefore, all diagnostic features of ''T. brauni'' are based on the skull.
Autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...
include (1) temporal sulcus of lateral line with two portions, (2) occipital sulcus continuous, (3) pre-orbital region slightly shorter than half skull length (0.43–0.49), and (4) interorbital distance wide (interorbital distance/ skull length: 0.15–0.2). The description is based only on referred specimens, as no
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 sever ...
was ever designated and the
syntype In biological nomenclature, a syntype is any one of two or more biological types that is listed in a description of a taxon where no holotype was designated. Precise definitions of this and related terms for types have been established as part of ...
s described by Burmeister cannot be identified based on the scant details of his description; however, because they may exist, either within public or private collections, no
neotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
designation is warranted at present. ''Trematosaurus galae'' differs from ''T. brauni'' in (1) presence of well-pronounced lacrimal and zygomatic flexures of canals of the lateral line, (2) connection of both branches of the temporal groove at the ossification center of the supratemporal, and (3) in the presence of a supplementary groove (sulcus buccalis transversus) on the squamosal. The more questionably valid ''T. thuringiensis'' differs only in having larger orbits and a narrower skull table than the type species. Given the large sample size of ''T. brauni'', its ontogeny can be characterized, exhibiting features such as decreased orbit size and skull width but not other features such as broadening of the interorbital region or increased preorbital length, which occur in other temnospondyls. Observations of more fragmentary material of ''T. galae'' indicate that specifically the prenarial region and the postorbital regions become longer, along with increased development of other features such as the basioccipital and ornamentation on the parasphenoid replacing a shagreen of denticles.


Classification

Below is a cladogram from Steyer (2002) showing the
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
relationships of trematosaurids:


References

{{Taxonbar, from=Q3776858 Triassic temnospondyls of Europe Trematosaurines Taxa named by Hermann Burmeister Prehistoric amphibian genera