Triassurus

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Triassurus
Temporal range: Late Triassic,
~235–222  Ma
Triassurus flipped.png
Sketch of the holotype
Triassurus NT.png
Life restoration
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Clade: Caudata
Family: Triassuridae
Ivakhnenko, 1978
Genus: Triassurus
Ivakhnenko, 1978
Species:
T. sixtelae
Binomial name
Triassurus sixtelae
Ivakhnenko, 1978

Triassurus is an extinct genus of amphibian, and the oldest member of Caudata (salamanders and close relalatives). It is known from the Middle to Upper Triassic (Ladinian-Carnian) aged Madygen Formation in Kyrgyzstan. [1] [2] The type species is T. sixtelae. [1]

Contents

Description

The holotype specimen is a partial and poorly preserved skeleton (PIN-2584/10), including the skull. Holotype specimen had tiny skull just 3.8 mm (0.15 in) long, but it was probably a larva: the neural arches of the vertebrae were still paired and no vertebral centers show any degree of ossification. The skull closely resembles that of current salamanders, especially as regards the long space in the joint of the maxillary bones and the lack of bone connection between the pterygoid and the maxilla. There were about 20 presacral vertebrae, while the legs were small. [1] [2] In 2020, a more complete adult specimen (FG 596/V/20) with 11 mm (0.43 in) long skull was described. [2]

Classification

Triassurus was first described in 1978, [1] based on a fossil found in the Madygen Formation in Kyrgyzstan. The bizarre planatory reptiles Sharovipteryx and Longisquama were also found in the same formation. [3] [4] Triassurus was initially described as the oldest salamander, based mainly on the characteristics of the skull. Some vertebral characteristics, in reality, would lead not only to primitive salamanders such as Hynobius but also to the larval forms of frogs and to the temnospondyls. Furthermore, the cheek area is similar to branchiosaurs. [5] In any case, Triassurus remains the most salamander-like Triassic amphibian fossil. [1] In 2020 Triassurus was definitely determined to a caudatan, based on four apomorphies shared with salamanders: "parasphenoid shape and dorsal surface, with a V-shaped anterior depression, an unpaired posteromedial crest, and a radial arrangement of furrows; parietal not plate-like and rectangular but L-shaped; squamosal forming a straight transverse strut with slightly expanded lateral end and well-expanded medial end, without squamosal embayment; and straight scapula with expanded ends". [2] In 2022 another phylogenetic analysis, that included members of Dissorophoidea, caecilians, frogs, as well as both living and fossil salamanders, recovered Triassurus as a stem-group caudatan, outside the crown group of modern salamanders. [6]

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The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia, the Caudata, and the Gymnophiona.

<span class="mw-page-title-main">Caudata</span> Clade of amphibians

The Caudata are a group of amphibians containing the extant salamanders and all extinct species of amphibians more closely related to salamanders than to frogs. They are typically characterized by a superficially lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults.

<span class="mw-page-title-main">Caecilian</span> Order of amphibians

Caecilians are a group of limbless, vermiform (worm-shaped) or serpentine (snake-shaped) amphibians with small or sometimes nonexistent eyes. They mostly live hidden in soil or in streambeds, and this cryptic lifestyle renders caecilians among the least familiar amphibians. Modern caecilians live in the tropics of South and Central America, Africa, and southern Asia. Caecilians feed on small subterranean creatures such as earthworms. The body is cylindrical and often darkly coloured, and the skull is bullet-shaped and strongly built. Caecilian heads have several unique adaptations, including fused cranial and jaw bones, a two-part system of jaw muscles, and a chemosensory tentacle in front of the eye. The skin is slimy and bears ringlike markings or grooves and may contain scales.

<span class="mw-page-title-main">Labyrinthodontia</span> Paraphyletic group of tetrapodomorphs

"Labyrinthodontia" is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras. Traditionally considered a subclass of the class Amphibia, modern classification systems recognize that labyrinthodonts are not a formal natural group (clade) exclusive of other tetrapods. Instead, they consistute an evolutionary grade, ancestral to living tetrapods such as lissamphibians and amniotes. "Labyrinthodont"-grade vertebrates evolved from lobe-finned fishes in the Devonian, though a formal boundary between fish and amphibian is difficult to define at this point in time.

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Saltoposuchus is an extinct genus of small, long-tailed crocodylomorph reptile (Sphenosuchia), from the Norian of Europe. The name translated means "leaping foot crocodile". It has been proposed that Terrestrisuchus gracilis and Saltoposuchus connectens represent different ontogenetic stages of the same genus. Saltoposuchus was commonly referred to in popular literature as the ancestor to dinosaurs; however, recent scientific research shows that this is not the case.

<i>Sharovipteryx</i> Extinct genus of reptiles

Sharovipteryx is a genus of early gliding reptiles containing the single species Sharovipteryx mirabilis. It is known from a single fossil and is the only glider with a membrane surrounding the pelvis instead of the pectoral girdle. This lizard-like reptile was found in 1965 in the Madygen Formation, Dzailauchou, on the southwest edge of the Fergana Valley in Kyrgyzstan, in what was then the Asian part of the U.S.S.R. dating to the middle-late Triassic period. The Madygen horizon displays flora that put it in the Upper Triassic. An unusual reptile, Longisquama, was also found there.

<i>Longisquama</i> Extinct genus of reptiles

Longisquama is a genus of extinct reptile. There is only one species, Longisquama insignis, known from a poorly preserved skeleton and several incomplete fossil impressions from the Middle to Late Triassic Madygen Formation in Kyrgyzstan. It is known from the type fossil specimen, slab and counterslab and five referred specimens of possible integumentary appendages. All specimens are in the collection of the Paleontological Institute of the Russian Academy of Sciences in Moscow.

<i>Riojasuchus</i> Extinct genus of reptiles

Riojasuchus is an extinct genus of ornithosuchid archosaur from the Late Triassic (Norian) of Argentina. Ornithosuchidae was a widespread family of facultatively bipedal pseudosuchians with adaptations for scavenging. Riojasuchus is notable as one of the youngest and most complete members of the family. The type and only known species, Riojasuchus tenuisceps, was named and described by José Bonaparte in 1967. It was one of the first of many well-preserved Triassic archosaurs to be discovered in Argentina. The holotype specimen, PVL 3827, was found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina.

<i>Metoposaurus</i> Extinct genus of amphibians

Metoposaurus meaning "front lizard" is an extinct genus of stereospondyl temnospondyl amphibian, known from the Late Triassic of Germany, Italy, Poland, and Portugal. This mostly aquatic animal possessed small, weak limbs, sharp teeth, and a large, flat head. This highly flattened creature mainly fed on fish, which it captured with its wide jaws lined with needle-like teeth. Many Metoposaurus mass graves have been found, probably from creatures that grouped together in drying pools during drought.

<i>Mecistotrachelos</i> Extinct genus of reptiles

Mecistotrachelos is an extinct genus of gliding reptile from the Late Triassic of Virginia. It is generally interpreted as an archosauromorph, distantly related to crocodylians and dinosaurs. The type and only known species is M. apeoros. This specific name translates to "soaring longest neck", in reference to its gliding habits and long neck. This superficially lizard-like animal was able to spread its lengthened ribs and glide on wing-like membranes. Mecistotrachelos had a much longer neck than other gliding reptiles of the Triassic such as Icarosaurus and Kuehneosaurus. It was probably an arboreal insectivore.

<span class="mw-page-title-main">Albanerpetontidae</span> Family of amphibians

The Albanerpetontidae are an extinct family of small amphibians, native to the Northern Hemisphere during the Mesozoic and Cenozoic. The only members of the order Allocaudata, they are thought to be allied with living amphibians belonging to Lissamphibia. Despite a superficially salamander-like bodyform, their anatomy is strongly divergent from modern amphibians in numerous aspects. The fossil record of albanerpetontids spans over 160 million years from the Middle Jurassic to the beginning of the Pleistocene, about 2.13–2 million years ago.

<i>Cryobatrachus</i> Extinct genus of amphibians

Cryobatrachus is an extinct genus of temnospondyl amphibian from the Early Triassic of Antarctica. The type species is Cryobatrachus kitchingi. It is known from a partial skull and an imprint of the skull roof, both found in the Fremouw Formation of the Transantarctic Mountains at about 85° south latitude and described in 1974. Many small bone fragments have also been identified, although they cannot be attributed with certainty to C. kitchingi. Cryobatrachus has been classified in the family Lydekkerinidae, as it is similar in appearance to the genus Lydekkerina from South Africa. Because only a small number of features distinguish it from other lydekkerinids, Cryobatrachus kitchingi has more recently been considered a nomen dubium, meaning that its distinction from other better-known species may be unwarranted.

Kokartus is an extinct genus of prehistoric stem-group salamander (Caudata) from the Middle Jurassic Balabansai Formation of Kyrgyzstan.

<span class="mw-page-title-main">Salientia</span> Order of amphibians

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Susan Elizabeth Evans is a British palaeontologist and herpetologist. She is the author or co-author of over 100 peer-reviewed papers and book chapters.

<span class="mw-page-title-main">Karauridae</span> Extinct family of amphibians

The Karauridae are a family of stem-group salamanders (Caudata) that are known from the Middle Jurassic to Early Cretaceous in Central Asia, Northern Asia and Western Europe. The family includes four members: Karaurus from the Middle-Late Jurassic Karabastau Formation of Kazakhstan, Kokartus from the Middle Jurassic Balabansai Formation of Kyrgyzstan, Marmorerpeton from the Middle Jurassic Forest Marble Formation of England and Kilmaluag Formation of Scotland, and Kuzbassia from the Early Cretaceous (Aptian) Ilek Formation. The members are some of the oldest known salamanders. The family is united by several morphological characters, including sculptured skull roof bones. Like some modern salamanders, karaurids were neotenic. Members of the family likely fed via suction feeding on small fish and invertebrates. The Early Cretaceous Siberian Kulgeriherpeton has been suggested to be a karaurid by some authors.

Kyrgyzsaurus is an extinct genus of drepanosaurid reptile known from the Triassic of southwestern Kyrgyzstan. It was discovered in the Madygen Formation.

The Madygen Formation is a Late Triassic (Carnian) geologic formation and Lagerstätte in the Batken and Osh Regions of western Kyrgyzstan, with minor outcrops in neighboring Tajikistan and Uzbekistan. The conglomerates, sandstones and mudstones of the 560 m (1,840 ft) thick formation were deposited in terrestrial lacustrine, alluvial, fluvial and deltaic environments.

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References

  1. 1 2 3 4 5 MF Ivakhnenko. (1978). Tailed amphibians from the Triassic and Jurassic of Middle Asia. Paleontological Journal 1978 (3): 84-89 Estes, R. 1981. Gymnophiona, Caudata. Pp. 1–115 in P. Wellnhofer (ed.). Handbuch der Paldoherpetologie, Vol. 2. Stuttgart: Gustav Fischer Verlag.
  2. 1 2 3 4 Schoch, Rainer R.; Werneburg, Ralf; Voigt, Sebastian (2020). "A Triassic stem-salamander from Kyrgyzstan and the origin of salamanders". Proceedings of the National Academy of Sciences. 117 (21): 11584–11588. Bibcode:2020PNAS..11711584S. doi: 10.1073/pnas.2001424117 . PMC   7261083 . PMID   32393623.
  3. Sharov, A.G. (1970). "A peculiar reptile from the lower Triassic of Fergana". Paleontologicheskii Zhurnal (1): 127–130.
  4. Sharov, A. G. 1971. New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. – Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
  5. R. Estes. 1981. Handbuch der Paläoherpetologie/Encyclopedia of Paleoherpetology. Part 2. Gymnophiona, Caudata. Gustav Fischer Verlag, Stuttgart xv-115
  6. Jones, Marc E. H.; Benson, Roger B. J.; Skutschas, Pavel; Hill, Lucy; Panciroli, Elsa; Schmitt, Armin D.; Walsh, Stig A.; Evans, Susan E. (2022-07-11). "Middle Jurassic fossils document an early stage in salamander evolution". Proceedings of the National Academy of Sciences. 119 (30). doi: 10.1073/pnas.2114100119 . ISSN   0027-8424.