HOME

TheInfoList



OR:

Thalattosauria ( Greek for "sea lizards") is an extinct
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
of prehistoric
marine reptile Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. The earliest marine reptile mesosaurus (not to be confused with mosasaurus), arose in the Permian period during the ...
s that lived in the middle to late Triassic period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies:
Askeptosauroidea Askeptosauroidea is a superfamily of thalattosaurs, a Triassic group of marine reptiles. Askeptosauroidea is one of two major subgroups of Thalattosauria, the other being Thalattosauroidea. It includes the family Askeptosauridae and a more basal ...
and Thalattosauroidea. Askeptosauroids were endemic to the Tethys Ocean, their fossils have been found in Europe and China, and they were likely semiaquatic fish eaters with straight snouts and decent terrestrial abilities. Thalattosauroids were more specialized for aquatic life and most had unusual downturned snouts and crushing dentition. Thalattosauroids lived along the coasts of both Panthalassa and the Tethys Ocean, and were most diverse in China and western North America. The largest species of thalattosaurs grew to over 4 meters (13 feet) in length, including a long, flattened tail utilized in underwater propulsion. Although thalattosaurs bore a superficial resemblance to
lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s, their exact relationships are unresolved. They are widely accepted as diapsids, but experts have variously placed them on the reptile family tree among Lepidosauromorpha ( squamates, rhynchocephalians and their relatives),
Archosauromorpha Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liza ...
(
archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
s and their relatives), ichthyosaurs, and/or other marine reptiles.


Description

Thalattosaurs have moderate adaptations to marine lifestyles, including long, paddle-like tails and slender bodies with more than 20 dorsal vertebrae. There are few unique traits of the postcranial skeleton shared by all thalattosaurs, but the skeleton is still useful for distinguishing between askeptosauroids and thalattosauroids. Askeptosauroids are characterized by elongated necks with short neural spines and at least 11 vertebrae, while thalattosauroids have shorter necks sometimes involving as few as four vertebrae. Thalattosauroids also have tall neural spines on their neck, back, and especially the tail vertebrae, increasing the surface area for swimming via lateral undulation. Thalattosauroids additionally possess short, wide limb bones poorly adapted for movement on land. In this superfamily, the
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
is widest near the shoulder, the femur is widest near the knee, the radius is reniform (" kidney-shaped"), and
phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...
are long and plate-like. Askeptosauroids retain hourglass-shaped limb bones like land reptiles, but even they share specializations with thalattosauroids such as a short tibia and fibula, with the latter expanding near the ankle.


Skull

Thalattosaurs are diapsid reptiles, meaning that they have temporal fenestrae, two holes in the head behind the orbit (eye socket). However, many thalattosaurs have a vestigial upper temporal fenestra which is slit-like, and some have it fully closed up by surrounding bones. Thalattosaurs lack a quadratojugal bone, leaving the lower temporal fenestra open from below. They also lack postparietal and tabular bones, while the squamosal bone is small, the supratemporal bone is extensive, and the quadrate bone is large. When seen from above, the rear edge of the skull bears a large, triangular embayment that reaches further forwards than the quadrates. Thalattosaurs have a rostrum (snout) significantly longer than the portion of the skull behind the eyes. A majority of this length is formed from the premaxillary bones, and the nares (nostril holes) are shifted back close to the eyes. The premaxillae stretch back very far and are incised into the frontal bones. This leads to an unusual trait that is characteristic of thalattosaurs, where the left and right nasal bones are separated from each other and restricted to a small portion of the snout near the nares. The lacrimal bone is typically lost or fused to the large crescent-shaped prefrontal bone in front of the orbit, mirroring the postfrontal bone which is usually fused to the three-pronged postorbital bone behind the orbit.
Askeptosauroidea Askeptosauroidea is a superfamily of thalattosaurs, a Triassic group of marine reptiles. Askeptosauroidea is one of two major subgroups of Thalattosauria, the other being Thalattosauroidea. It includes the family Askeptosauridae and a more basal ...
have narrow, straight-edged snouts which are often elongated and filled with conical teeth. One askeptosauroid, '' Endennasaurus'', is entirely toothless while another, '' Miodentosaurus'', has a short, blunt snout. Most members of the second thalattosaur group, Thalattosauroidea, have more distinctive downturned snouts. ''
Clarazia ''Clarazia'' is an extinct genus of thalattosaur from the Middle Triassic of Monte San Giorgio in Switzerland. It is represented by a single type species In zoological nomenclature, a type species (''species typica'') is the species name with ...
'' and '' Thalattosaurus'' both have snouts that taper into a narrow tip. Most of the snout is straight, but premaxillae at the tip are downturned. '' Xinpusaurus'' and ''
Concavispina ''Concavispina'' is an extinct genus of thalattosaur reptile from the early Late Triassic (Carnian stage) Xiaowa Formation of Guangling, Guizhou, southern China. It contains a single species, ''Concavispina biseridens''. It is known only from th ...
'' also have downturned premaxillae, but the end of the maxillae are sharply upturned, forming a notch in their skull. In '' Hescheleria'' (and potentially '' Nectosaurus'' and '' Paralonectes''), the premaxillae are abruptly downturned at the end of the snout, nearly forming a right angle with the rest of the jaw. In these forms, the end of the snout is a toothy hook separated from the rest of the jaw by a space called a diastema. Thalattosauroids also have
heterodont dentition In anatomy, a heterodont (from Ancient Greek, Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology (biology), morphology. In vertebrates, heterodont pertains to animals where teeth are differentiate ...
, with pointed piercing teeth at the front of the snout and low crushing teeth further back. The exception to this rule is ''
Gunakadeit ''Gunakadeit'' is an extinct genus of thalattosaur. It is known from a single species, ''Gunakadeit joseeae'', which is based on an articulated and mostly complete skeleton from the late Triassic (middle Norian) Hound Island Volcanics of Alaska. ...
'', which has a straight snout and many slender teeth. Thalattosaurs often have a pronounced retroarticular process at the rear of the mandible. Thalattosauroids are more specialized than askeptosauroids in jaw anatomy, as they have evolved a large peak-like coronoid bone and an
angular bone The angular is a large bone in the lower jaw (mandible) of amphibians and reptiles (birds included), which is connected to all other lower jaw bones: the dentary (which is the entire lower jaw in mammals), the splenial, the suprangular, and the art ...
that extends far forwards along the lower edge of the jaw. Palatal dentition is extensive in thalattosauroids but absent in askeptosauroids.


Paleobiology

Thalattosaurs are only known from marine deposits, indicating that they were all primarily aquatic reptiles. The retracted nostrils and long, paddle-shaped tail are further evidence for aquatic habits. Thalattosauroids seemingly spent all of their time in the water, with short, wide limbs, poorly developed wrist and ankle bones, and tall vertebrae adapted for swimming via lateral undulation. Even so, they retained strong claws and functional digits which had not transformed into flippers, in contrast to ichthyosaurs and
sauropterygians Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became ...
. Unlike these other marine reptiles, there is no evidence that thalattosaurs fully adapted to a pelagic life out in the open ocean, and instead they probably all lived in warm waters close to the coast. Askeptosauroids had stronger limbs more typical of terrestrial reptiles, indicating they would have been capable of moving around on land to some extent. They likely primarily used their tails when swimming, while thalattosauroids may have utilized their body and tail in conjunction. Thalattosaurs had diverse diets, though they probably all involved marine animals in one way or another. '' Endennasaurus'' probably predated small animals like fish fry or small crustaceans due to its lack of teeth. Various thalattosauroids (like '' Thalattosaurus'', '' Xinpusaurus'', and ''
Concavispina ''Concavispina'' is an extinct genus of thalattosaur reptile from the early Late Triassic (Carnian stage) Xiaowa Formation of Guangling, Guizhou, southern China. It contains a single species, ''Concavispina biseridens''. It is known only from th ...
'') had large fang-like teeth at the front of the mouth and thick button-like teeth at the back of the mouth. Based on Massare (1987)'s technique of correlating diet with tooth shape, the taller teeth were suited for a "crunching" diet, involving armored fish, large crustaceans, and thin-shelled ammonites. The low, robust teeth would have been useful for a "crushing" diet specialized in large molluscs or other thick-shelled prey. ''
Gunakadeit ''Gunakadeit'' is an extinct genus of thalattosaur. It is known from a single species, ''Gunakadeit joseeae'', which is based on an articulated and mostly complete skeleton from the late Triassic (middle Norian) Hound Island Volcanics of Alaska. ...
'''s slender teeth correlated with the "Pierce II" guild of Massare (1987), indicating it likely fed on soft, fast-moving fish and squid. It also had a large hyoid apparatus which may have played a role in suction feeding. Thalattosaurs also fell prey to other marine reptiles: the torso of a ~4 meter (13 feet) long ''Xinpusaurus xingyiensis'' has been found within the body cavity of a 5 meter (16 feet) long skeleton of the predatory ichthyosaur '' Guizhouichthyosaurus.'' This is the oldest known predatory interaction between marine reptiles, and ''Xinpusaurus'' may also be the largest prey item preserved within another marine reptile.


Distribution

It is not certain where thalattosaurs originated from. During the Triassic period, the earth had one giant supercontinent, Pangaea, which was surrounded by the superocean Panthalassa. The eastern portion of Pangaea was incised by a massive tropical inland sea, the Tethys Ocean, which extended all the way from China to Western Europe. While thalattosauroids are known from worldwide Triassic marine deposits, askeptosauroids are only known in Tethyan deposits. Assuming '' Endennasaurus'' and '' Askeptosaurus'' were the most
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...
askeptosauroids, Askeptosauroidea would have originated in the Western Tethys Ocean, now the Alpine region of Europe. However, if '' Miodentosaurus'' is more basal, a Western Tethys (European) origin would be significantly less likely. Although the
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
to Thalattosauria is still debated, one possibility, the icthyosauromorphs, seemingly evolved in the Eastern Tethys (China) during the early Triassic or earlier. The oldest known thalattosauroids (''Thalattosaurus'', '' Paralonectes'', and ''
Agkistrognathus ''Agkistrognathus'' is an extinct genus of thalattosaurian which lived in the early to middle Triassic of British Columbia, Canada. There is only one species known in this genus, ''Agkistrognathus campbelli''. The genus name translates to "hook j ...
'' of British Columbia's Sulphur Mountain Formation) lived in eastern Panthalassa, along what is now the western coast of North America. Müller (2005, 2007) argued that at least one branch of thalattosauroids had managed to spread worldwide early in their evolution. However, this is based on the hypothesis that '' Nectosaurus'' (from California), ''Xinpusaurus'' (from China), and an unnamed species from Austria formed a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
basal to other thalattosaurs, a classification scheme which contrasts with many other studies. The worldwide distribution of Thalattosauroidea is intriguing considering that thalattosaurs are considered to be poorly adapted for traversing open oceans, which would have been a necessity for spreading between the eastern coast of Panthalassa and the Tethys Ocean. Coastal "refuges" such as volcanic island arcs and guyots may have facilitated the ability of thalattosaurs to spread between ocean basins. '' Hescheleria''-like forms were previously only reported from North America and Europe, but in 2021 a ''Hescheleria''-like snout fragment was reported from China, indicating that they also had a widespread distribution. Trans-Panthalassa connections are also observed in other Triassic marine life such as pistosaurs and ammonites. Evidently thalattosaurs were capable of dispersing throughout major marine regions multiple times before the group's extinction, with thalattosauroids likely more prolific at spreading than askeptosauroids due to their greater aquatic adaptations.


Classification


Early hypotheses

When first named by Merriam in 1904, Thalattosauria was only known by the species ''Thalattosaurus alexandrae''. Based primarily on the overall skull shape, it was hypothesized to have been close to the reptile order
Rhynchocephalia Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the tuatara (''Sphenodon punctatus'') of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a diverse g ...
, which includes ''Sphenodon'' (the living tuatara). Nevertheless, ''Thalattosaurus'' was recognized as distinct enough to be given its own order, and was tentatively grouped along with Rhynchocephalia in the group Diaptosauria, a collection of various "primitive" reptiles now known to be polyphyletic. Within Diaptosauria, thalattosaurs were also considered very closely related to
choristoderes Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the late Miocene (168 to ...
and "Proganosauria" (
parareptiles Parareptilia ("at the side of reptiles") is a subclass or clade of basal sauropsids (reptiles), typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near t ...
). Comparisons were also made with Parasuchia ( phytosaurs), Lacertilia (
lizards Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...
), and '' Proterosuchus'', but dismissed as incompatible with proposed evolutionary schemes. Further discussion by Merriam (1905) considered a relationship with ichthyosaurs due to their similar ecology, but questioned why their skull and vertebral anatomy would diverge so widely if they had a close common ancestor. He proposed that potential similarities were best explained as convergent evolution. The possibility that thalattosaurs diverged from reptiles close to lizards (such as '' Paliguana'') was described in more detail, with thalattosaurs serving as an short-lived early attempt for near-lizards to return to the sea, an evolutionary process later repeated more successfully when mosasaurs evolved from true lizards. Nevertheless, Merriam found no clear evidence that any previously known reptile group was directly ancestral to thalattosaurs or vice versa. They were probably descended from land-dwelling Permian reptiles, and not closely related to other marine reptile groups which first evolved in the Triassic. Later 20th-century workers typically placed thalattosaurs close to rhynchocephalians or squamates as part of the group now known as Lepidosauromorpha.


Modern classification and outgroup relations

The rising popularity of cladistics in the late 1980s had some effects on thalattosaur classification. Continued research has helped cement some aspects of reptile classification, such as how Sauria (a major
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
of diapsids including all living reptiles) split in the Permian into two branches: Lepidosauromorpha (which leads to lizards, snakes, and the tuatara) and
Archosauromorpha Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liza ...
(which leads to crocodilians and dinosaurs, including birds). While many paleontologists still consider thalattosaurs probable lepidosauromorphs, a few studies (such as a phylogenetic analysis by Evans, 1988) have instead suggested that they may be on the archosauromorph branch of Sauria. Rieppel (1998)'s re-evaluation of the thalattosaur-like pachypleurosaur ''
Hanosaurus ''Hanosaurus'' is an extinct genus of marine reptiles that existed during the Triassic period in what is now China. It was described by Young in 1972, and the type species is ''Hanosaurus hupehensis''. Its affinities are unclear; it has been bot ...
'' argued that thalattosaurs have affinities with the aquatic reptile order Sauropterygia, which itself is aligned with turtles within an expansive interpretation of Lepidosauromorpha. An analysis by
Müller Müller may refer to: * ''Die schöne Müllerin'' (1823) (sometimes referred to as ''Müllerlieder''; ''Müllerin'' is a female miller) is a song cycle with words by Wilhelm Müller and music by Franz Schubert * Doctor Müller, fictional character ...
(2004) has even considered thalattosaurs to belong just outside of Sauria. Unusually, thalattosaurs have an affinity to shift near ichthyosaurs (in the group Ichthyosauromorpha) when certain basal saurians or near-saurians are excluded from the data set. Some analyses derived from Müller (2004) group thalattosaurs in a "marine superclade" with ichthyosauromorphs and sauropterygians, and sometimes with turtles, archosauromorphs, or lepidosauromorphs as well. However, cladograms generated by these analyses change in unpredictable ways through alterations to their methodology (such as including or excluding aquatic adaptations or switching between
parsimony Parsimony refers to the quality of economy or frugality in the use of resources. Parsimony may also refer to * The Law of Parsimony, or Occam's razor, a problem-solving principle ** Maximum parsimony (phylogenetics), an optimality criterion in p ...
and
bayesian inference Bayesian inference is a method of statistical inference in which Bayes' theorem is used to update the probability for a hypothesis as more evidence or information becomes available. Bayesian inference is an important technique in statistics, a ...
), leading some to have concerns over the validity of the "marine superclade". While thalattosaurs are almost certainly diapsids, the large degree of uncertainty surrounding their
outgroup Outgroup may refer to: * Outgroup (cladistics), an evolutionary-history concept * Outgroup (sociology), a social group {{disambig ...
relations has led most modern paleontologists to classify them as Diapsida '' incertae sedis''.


Ingroup relations

One of the first phylogenetic analyses specifically focusing on thalattosaurs was part of Nicholls (1999)'s reevaluation of '' Thalattosaurus'' and '' Nectosaurus''. She used a restricted definition of Thalattosauria which referred to a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
including all reptiles more closely related to ''Nectosaurus'' and '' Hescheleria'' than to '' Endennasaurus'' or ''Askeptosaurus''. The more inclusive group including ''Askeptosaurus'', ''Endennasaurus'', and traditional thalattosaurs was given the name Thalattosauriformes. However, most studies focusing on the group have preferred to retain a broader definition of Thalattosauria equivalent to Nicholls' Thalattosauriformes clade, including reptiles close to both ''Askeptosaurus'' and ''Thalattosaurus''. In these studies, Thalattosauria is divided into two branches, one leading to relatives of ''Askeptosaurus'' and the other leading to relatives of ''Thalattosaurus''. The clade containing reptiles closer to ''Thalattosaurus'' than to askeptosaurids is given the name Thalattosauroidea (and sometimes called Thalattosauridea). Meanwhile, the clade containing reptiles closer to askeptosaurids is termed
Askeptosauroidea Askeptosauroidea is a superfamily of thalattosaurs, a Triassic group of marine reptiles. Askeptosauroidea is one of two major subgroups of Thalattosauria, the other being Thalattosauroidea. It includes the family Askeptosauridae and a more basal ...
''''or Askeptosauridea. Subsequent studies since Nicholls (1999) started to include more taxa, including newly described Chinese taxa such as '' Anshunsaurus'' and '' Xinpusaurus''.'''' However, uncertainty over ''Endennasaurus'''s thalattosaurian ancestry led to it being excluded from these analyses. After Müller ''et al''. (2005) re-affirmed that ''Endennasaurus'' was closely related to ''Askeptosaurus'', all thalattosaurs known at the time were finally combined into phylogenetic analyses. Studies by Rieppel, Liu, Cheng, Wu, and others continued to identify new Chinese taxa such as '' Miodentosaurus'' and various species of ''Anshunsaurus'' and ''Xinpusaurus'', though homoplasy in these new taxa has led to little resolution in the structure of the two major branches of Thalattosauria. In an attempt to remedy this problem, new phylogenetic analyses were developed by Liu ''et al''. (2013) during the description of ''
Concavispina ''Concavispina'' is an extinct genus of thalattosaur reptile from the early Late Triassic (Carnian stage) Xiaowa Formation of Guangling, Guizhou, southern China. It contains a single species, ''Concavispina biseridens''. It is known only from th ...
'', and Druckenmiller ''et al.'' (2020) during the description of ''
Gunakadeit ''Gunakadeit'' is an extinct genus of thalattosaur. It is known from a single species, ''Gunakadeit joseeae'', which is based on an articulated and mostly complete skeleton from the late Triassic (middle Norian) Hound Island Volcanics of Alaska. ...
''. The internal relationships of thalattosaurs is still considered tentative and inconclusive, although the fundamental structure of the group (a monophyletic Thalattosauria clade split into askeptosauroids and thalattosauroids) is very stable. Some paleontologists have attempted to divide thalattosaurs into families. One family, Askeptosauridae, is typically considered to include ''Askeptosaurus'' and ''Anshunsaurus,'' with a few studies also placing ''Miodentosaurus'' or ''Endennasaurus'' within it. Another family, Thalattosauridae, was originally used to group ''Thalattosaurus'' and ''Nectosaurus'', was later redefined to exclude ''Nectosaurus'', and later still encompassed practically all thalattosauroids. Many thalattosaur-focused paleontologists avoid using family names due to their inconsistent usage and questionable validity. The cladogram presented here is based on the largest and most recent analysis of thalattosaur ingroup relations, Druckenmiller ''et al.'' (2020).


List of genera

Other thalattosaurs include unnamed or indeterminate species from the
Kössen Formation The Kössen Formation is a Late Triassic (Rhaetian-age) geological formation in the Northern Calcareous Alps of Austria and Germany, in the Tiroler-Lech Nature Park. During the Late Triassic, the area now occupied by the Northern Calcareous Alps w ...
of Austria, the Sulphur Mountain and
Pardonet Formation The Schooler Creek Group is a Stratigraphy, stratigraphic unit of Middle Triassic, Middle to Late Triassic (Ladinian to Norian) Geochronology, age in the Western Canadian Sedimentary Basin. It is present in northeastern British Columbia. It was nam ...
s of British Columbia, the
Natchez Pass Formation Natchez may refer to: Places * Natchez, Alabama, United States * Natchez, Indiana, United States * Natchez, Louisiana, United States * Natchez, Mississippi, a city in southwestern Mississippi, United States * Grand Village of the Natchez, a site o ...
of Nevada, and the
Vester Formation The Vester Formation is a geologic formation in Oregon which preserves fossils dating back to the Triassic period. The partial skeleton of a new genus of basal thalattosaur has been recovered from the Brisbois Member of this formation.Metz, Eric ...
of Oregon. ''
Blezingeria ''Blezingeria'' is an extinct genus of marine reptile from the Middle Triassic of Germany. The type and only species ''Blezingeria ichthyospondyla'' was named by German paleontologist Eberhard Fraas in 1896. It is known from many isolated bones ...
'', a fragmentary marine reptile from the Muschelkalk of Germany, has also been considered a thalattosaur by some authors but this assignment is uncertain at best. '' Neosinasaurus'' and '' Wayaosaurus'', a pair of poorly-known reptiles from the Xiaowa Formation of China, have also been considered thalattosaurs. Thalattosaurian fragments are known from Spanish Muschelkalk. A previously unnamed specimen from Alaska was described as ''
Gunakadeit ''Gunakadeit'' is an extinct genus of thalattosaur. It is known from a single species, ''Gunakadeit joseeae'', which is based on an articulated and mostly complete skeleton from the late Triassic (middle Norian) Hound Island Volcanics of Alaska. ...
'' in 2020.


References

{{Taxonbar, from=Q1123322 Triassic reptiles Triassic first appearances Late Triassic extinctions