Thalattosaurus

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Thalattosaurus
Temporal range: Late Triassic, 235.0–221.5  Ma
Thalattosaurus alexandrae life restoration.jpg
Restoration of Thalattosaurus alexandrae
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order:† Thalattosauria
Family:† Thalattosauridae
Genus:† Thalattosaurus
Merriam, 1904
Type species
†Thalattosaurus alexandrae
Merriam, 1904
Species
  • †T. alexandrae(Merriam, 1904) (type)
  • †T. borealis(Nicholls and Brinkman, 1993)
  • †T. perrini?(Merriam, 1905)
  • †T. shastensis?(Merriam, 1905)

Thalattosaurus (pronounced: /θəˈlætəˌsɔːrəs/ , "tha-la-to-SORE-us") meaning "sea lizard," from the Attic Greek thalatta (θάλαττα), "sea," and sauros (σαῦρος), "lizard," is an extinct genus of marine reptile in the family Thalattosauroidea. They were aquatic diapsids that are known exclusively from the Triassic period. It was a 2–3 metres (6.6–9.8 ft) long shellfish-eating reptile with paddle-like limbs and a down-turned rostrum occurring in the Lower and Middle Triassic Sulphur Mountain Formation of British Columbia as well as the Upper Triassic Hosselkus Limestone of California. [1] [2] It has gained notoriety as a result of studies on general diapsid phylogeny. [3]

Although originally described as four distinct species by Merriam in 1905, one was proven to be T. alexandrae upon further inspection and another[ which? ] has a missing type specimen.[ citation needed ] Currently it is believed to include two known species; Thalattosaurus alexandrae and T. borealis.

Discovery and naming

The Hosselkus Limestone where remains of Thalattosaurus have been found Hosselkus limestone top Brock-Mountain.jpg
The Hosselkus Limestone where remains of Thalattosaurus have been found

In the summer of 1903 Annie Alexander led an expedition with Miss Edna Wemple, Eustace Furlong, Merriam John C, W.B. Esterly, and Mr. F.S. Ray to Shasta County where they discovered what they initially thought was Shastasaurus . One of the fossils were found in the North Fork of Squaw Creek (Triassic of the United States) in Shasta County, California. The environment it was found in was a shelly/skeletal limestone with a horizon composed largely of broken shells. It was estimated to be from the Hosselkus Limestone Formation from the Carnian period, dating from 235 to 221.5 million years ago. It was later collected by the University of California. The fossil found by Annie Alexander in 1903 had much of original bone in preorbital area gone, vomer was exposed, an incomplete mandible, two dorsal ribs and centra, and three articulated caudal vertebrae pressed against the vomer. [4]

After Merriam's further studies, it was categorized as a new species named Thalattosarus alexandrae. [5] The first thalattosaurs to be described were Thalattosaurus and Nectosaurus from the Upper Triassic of California by Merriam in 1904, 1905, and 1906. Thalattosaurus alexandrae was named by Merriam in 1904. Its name is Thalattosaurus meaning "sea lizard" and alexandrae in honor of Annie Alexander, an amateur paleontologist and patron to the University of California Museum of Paleontology. [6] This material was later reviewed by Nicholls in 1999. [7]

Originally four subtaxa of Thalattosaurus were classified; Thalattosaurus alexandrae, Thalattosaurus perrini, and Thalattosaurus shastensis by Merriam [8] but later additional examination of the type of T. shastensis suggested that it does not belong in the genus Thalattosaurus. It is still currently under study. The type skull of T. perrini has not been located, but the vomer figured by Merriam in 1905 did not differ from the vomer of T. alexandrae. [9]

In 1993, another species named Thalattosarus borealis was found in a talus slope near Wapiti Lake, British Columbia, in the Sulphur Mountain Formation. [4] [10] The environment, similar to the discovery of T. alexandrae, was also marine shale, and marl. This specimen was discovered and collected by the Royal Tyrrell Museum of Paleontology field crew. Thalattosaurus borealis was named after its Northern discovery location, with Thalattosaurus meaning "ocean lizard" and borealis coming from boreas (Greek word, βορέας) meaning "Northern." Discovered elements include the anterior part of skull, incomplete mandible, centra, isolated ribs, and left pterygoid. [10]

Description

A modern skull diagram of Thalattosaurus alexandrae Thalattosaurus skull diagram.png
A modern skull diagram of Thalattosaurus alexandrae

As noted by Merriam in 1905, the skull of the holotype, referred to as UCMP 9085, was preserved in four pieces. They were originally connected by calcite vein-filled cracks, but were separated during preparation. [8] Three of these four pieces found made up the rostrum. When aligned, the rostrum shape suggested dorsal curvature of the anterior end of the maxilla but ventral deflection in the anterior end of premaxilla. The prefrontal, however, came down ventrally under the margin of the maxilla and contacts the anterior tip of the suborbital process [10] A line drawn from the preserved anterior alveolar margin of the maxilla to the lower edge of the prefrontal showed that the ventral margin of the maxilla was straight, very similar to the rostral structure known of Clarazia . Upon further examination, the other characteristics found true of this fossil were a striated external surface of bone with smooth bone resembling "pseudodont teeth". The first of which was blunt, procumbent and short, the second was pointed and thinner, with the third (although the tip was broken) the thick base implied a blunt tooth. There was an additional broken stump which may suggest a fourth tooth. [8]

Phylogenetic interrelationships of Thalattosaurus is one of the better known from the thalattosaur genera. [11] When comparing T. borealis to the type species, T. alexandrae, the most apparent difference is size. Thalattosaurus borealis is much smaller, with the distance from the tip of the snout to the anterior edge of the orbit being less than 60mm. In T. alexandrae, however, this distance is almost 200mm. Initially a difference in age (juvenile vs. adult) was suspected but because the bone in the T. borealis specimen is thoroughly ossified and the caudal vertebral neural arches are fused to the centra, it was concluded that the specimen was a fully formed adult. The vomer of T. borealis also differs from the vomer of T. alexandrae in the type of dentition present. The vomer of T. alexandrae has two rows of teeth closely set anteriorly and divergent posteriorly with ten teeth per row. These are low-crowned, bulbous teeth that are set in sockets. The vomer of T. borealis, on the other hand, has six high, triangular teeth that are fused to the bone.

T. alexandrae had only a single row of teeth present but the vomer must have developed as a paired structure, so it can be assumed that there must have been more than a single row of teeth. The bone is split sagittally and it is possible that an additional row of teeth was present but broke away during preservation. However, there is no evidence of a paired, diverging tooth row like we see in T. alexandrae. The wide, button-like teeth on the dentary are characteristic of all three, Thalattosaurus, Clarazia, and Paralonectes. The posterior mandibular teeth of T. borealis differ from these genera, however, being set flush with the margin of the jaw. In both T. alexandrae and Clarazia the posterior, bulbous teeth are set slightly ventral and medial to the jaw margin. In all thalattosaurs found, the posterior end of the dentary bifurcates into two diverging processes (upper and lower). This can be distinguished from Clarazia in which these two process are almost equal in length whereas in T. borealis the ventral process is much longer than the upper. [1]

Down-turned snout

Original reconstruction of T. alexandrae skull by Merriam in 1905 incorrectly portraying a straight snout Thalattosaurus alexandrae Merriam.jpg
Original reconstruction of T. alexandrae skull by Merriam in 1905 incorrectly portraying a straight snout

Originally illustrated by Merriam in 1905, his reconstruction of the skull of T. alexandrae portrayed the rostrum as being straight and showed six conical, striated teeth on the premaxilla. This reconstruction has since been used in various books and published journals but is not accurate and has been corrected after Nicholls published on the subject in 1999. The premaxilla of the type specimen of T. alexandrae is distinctly curved. The three "teeth" previously illustrated are not teeth at all, but more like bony extensions of the premaxilla-"pseudodont" teeth similar to those found in T. borealis. This pseudodont dentition possibly suggests a possibility of a beak being present, similar to turtles and birds. [10]

Thalattosauroidea (which contains Clarazia and Thalattosaurus) have a relatively short rostrum, distinct from the elongate primitive condition, with convergent lateral margins that terminate in a pointed tip. It is also characteristic of their supratemporal to contact the frontal bone, having a heavy postorbital bar, diastema present that separates the premaxillary from the maxillary teeth, and a deep lower jaw. The Thalattosauroidea are easily distinguished by their down-turned snouts. In Clarazia and Thalattosaurus, the snouts taper to a narrow tip, with the premaxilla at the tip down-turned. [12]

Paleobiology

Thalattosaurus (left) with relative Nectosaurus (right) hunting shellfish. Thalattosauridae.jpg
Thalattosaurus (left) with relative Nectosaurus (right) hunting shellfish.

Thalattosaurus alexandrae was about around 2 meters (7 ft) long and an excellent swimmer. [10] Thalattosaur limbs were generally not paddle-like, but Thalattosaurus limbs were. It had a long flattened tail and claws possibly used to withstand the force of the surf when crawling up on shore. [5]

The Sulphur Mountain Formation, where remains of Thalattosaurus have been found, consists of a series of marine siltstones, silty limestones, and fine gained sandstones. All of the thalattosaur specimens from Wapiti Lake are preserved in sandstones, suggestive of shallow water conditions. It is likely that they often spent their time near the shore instead of deep-sea, open-water environments. Its remains were found in a marine shale and marl environment, which suggests it fed on marine life such as shelled animals. It had strong crushing teeth to crack the shells of its prey. [8]

Related Research Articles

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

Nectosaurus is a genus of thalattosaur which lived during the Late Triassic in what is now California. The type and only known species, Nectosaurus halius, was found in the Hosselkus Limestone and described by John C. Merriam in 1905, making it one of the first thalattosaurians known.

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

Askeptosaurus is an extinct genus of askeptosauroid, a marine reptile from the extinct order Thalattosauria. Askeptosaurus is known from several well-preserved fossils found in Middle Triassic marine strata in what is now Italy and Switzerland.

Clidastes is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like Mosasaurus and Prognathodon. Clidastes is known from deposits ranging in age from the Coniacian to the early Campanian in the United States.

<span class="mw-page-title-main">Thalattosauria</span> Extinct order of sea reptiles

Thalattosauria is an extinct order of prehistoric marine reptiles that lived in the Middle to Late Triassic. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea 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 lizards, their exact relationships are unresolved. They are widely accepted as diapsids, but experts have variously placed them on the reptile family tree among Lepidosauromorpha, Archosauromorpha, ichthyosaurs, and/or other marine reptiles.

Mesosuchus is an extinct genus of basal Rhynchosaur from early Middle Triassic deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5882, a partial skeleton, and from the paratypes SAM 6046, SAM 6536, SAM 7416 and SAM 7701 from the Aliwal North Euparkeria site. Mesosuchus is quite small, spanning around 30 cm in length. Mesosuchus was discovered and named by David Meredith Seares Watson in 1912.

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

Miodentosaurus is a genus of thalattosaurian from the Late Triassic of China. It is one of several thalattosaurs found in the Xiaowa Formation, also known as the Wayao Member of the Falang Formation. The genus name "Miodentosaurus" translates to "Few toothed-lizard" while the species name "brevis" means "short", in reference to its short snout.

Langobardisaurus is an extinct genus of tanystropheid archosauromorph reptile, with one valid species, L. pandolfii. Its fossils have been found in Italy and Austria, and it lived during the Late Triassic period, roughly 228 to 201 million years ago. Langobardisaurus was initially described in 1994, based on fossils from the Calcare di Zorzino Formation in Northern Italy. Fossils of the genus are also known from the Forni Dolostone of Northern Italy and the Seefeld Formation of Austria.

<i>Plesiotylosaurus</i> Extinct genus of lizards

Plesiotylosaurus, meaning "near Tylosaurus", is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like Mosasaurus and Prognathodon. The genus contains one species, Plesiotylosaurus crassidens, recovered from deposits of Middle Maastrichtian age in the Moreno Formation in California.

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

Vancleavea is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America. The type and only known species is V. campi, named by Robert Long & Phillip A Murry in 1995. At that time, the genus was only known from fragmentary bones including osteoderms and vertebrae. However, since then many more fossils have been found, including a pair of nearly complete skeletons discovered in 2002. These finds have shown that members of the genus were bizarre semiaquatic reptiles. Vancleavea individuals had short snouts with large, fang-like teeth, and long bodies with small limbs. They were completely covered with bony plates known as osteoderms, which came in several different varieties distributed around the body. Phylogenetic analyses by professional paleontologists have shown that Vancleavea was an archosauriform, part of the lineage of reptiles that would lead to archosaurs such as dinosaurs and crocodilians. Vancleavea lacks certain traits which are present in most other archosauriforms, most notably the antorbital, mandibular and supratemporal fenestrae, which are weight-saving holes in the skulls of other taxa. However, other features clearly support its archosauriform identity, including a lack of intercentra, the presence of osteoderms, an ossified laterosphenoid, and several adaptations of the femur and ankle bones. In 2016, a new genus of archosauriform, Litorosuchus, was described. This genus resembled both Vancleavea and more typical archosauriforms in different respects, allowing Litorosuchus to act as a transitional fossil linking Vancleavea to less aberrant archosauriforms.

<span class="mw-page-title-main">Askeptosauroidea</span> Extinct superfamily of reptiles

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 form called Endennasaurus.

<span class="mw-page-title-main">Askeptosauridae</span> Extinct family of reptiles

Askeptosauridae is a family of thalattosaurs within the superfamily Askeptosauroidea. Fossils have been found from Italy, Switzerland, and China. Askeptosaurids are distinguished from other thalattosaurs by their long necks and narrow skulls.

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

Anshunsaurus is a genus of thalattosaurs within the family Askeptosauridae. Fossils have been found from Middle Triassic deposits in Guizhou, China. Three species are known: the type species A. huangguoshuensis, the slightly older species A. wushaensis, and the species A. huangnihensis.

<span class="mw-page-title-main">Thalattosauroidea</span> Extinct superfamily of reptiles

Thalattosauroidea is a superfamily of thalattosaurs, a Triassic group of marine reptiles. It was named in 1904 by paleontologist John Campbell Merriam to include the genus Thalattosaurus from California. Thalattosauroids are one of two groups of Thalattosauria, the other being Askeptosauroidea. Thalattosauroids make up the "traditional" thalattosaurs with large downturned snouts, short necks, and long, paddle-like tails.

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

Concavispina is an extinct genus of thalattosaur reptile from the early Late Triassic Xiaowa Formation of Guangling, Guizhou, southern China. It contains a single species, Concavispina biseridens. It is known only from the holotype ZMNH M8804, a nearly complete 364 cm long skeleton. Concavispina can be differentiated from other thalattosaurs by possessing two rows of blunt teeth on the anterior part of the maxilla and a V-shaped notch on the dorsal margin of each neural spine in the dorsal (back) vertebrae. Both its generic and specific names refer to these autapomorphies, as Concavispina means "concave spine" and biseridens means "two rows of teeth". It is thought to be most closely related to Xinpusaurus, as both taxa share three derived characters: a maxilla that is curved upward at its anterior end, a humerus that is wider near the shoulder than near the elbow, and the presence of less than five cervicals.

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

Xinpusaurus is an extinct genus of thalattosaur from the Late Triassic of Guanling in Guizhou, China. Several species have been named since 2000: the type species X. suni along with the species X. bamaolinensis and X. kohi. A 2013 study proposed that all three species are synonymous with each other, in which case X. suni would be the only valid species, although a 2014 study argued that X. kohi was also valid. A fourth species, X. xingyiensis, was described in 2016.

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

Palatodonta is an extinct genus of neodiapsid reptile known from the early Middle Triassic of the Netherlands. It was initially described in 2013 as a basal placodontiform closely related to a group of marine reptiles called placodonts, characterized by their crushing teeth and shell-like body armor. Under this interpretation, Palatodonta is transitional between placodonts and less specialized reptiles. Like placodonts, it has a row of large teeth on its palate, but while these teeth are thick and blunt in placodonts, Palatodonta has palatal teeth that are thin and pointed. A 2023 study instead classified it as a sauropterygomorph and the sister taxon to Eusaurosphargis. In other words, it is close to, but not within, Sauropterygia.

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

Hescheleria is an extinct genus of thalattosaurian marine reptile from the Middle Triassic of Monte San Giorgio in Switzerland. It is represented by a single type species, H. ruebeli, which was named in 1936.

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 jaw" while the species name refers to Bob Campbell, who discovered the only known specimen.

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 Hound Island Volcanics of Alaska. Gunakadeit possessed a variety of features from the two major suborders of thalattosaurs, Askeptosauroidea and Thalattosauroidea, and it is considered the most basal member of the latter group. Despite this, it is also the youngest known thalattosaur genus, with the group going extinct at the end of the Triassic. Gunakadeit's basal position and relatively recent occurrence implies a 20-million-year ghost lineage connecting it to the rest of Thalattosauria. The skull ends in a sharply pointed and toothless tip like the askeptosauroid Endennasaurus, but unlike Endennasaurus, Gunakadeit had poorly developed joints and was likely exclusively aquatic in behavior.

<i>Kyhytysuka</i> Extinct marine reptile

Kyhytysuka is an extinct genus of ophthalmosaurian ichthyosaur from Early Cretaceous Colombia. The animal was previously assigned to the genus Platypterygius, but given its own genus in 2021. Kyhytysuka was a mid-sized ophthalmosaurian with heterodont dentition and several adaptations suggesting that it was a macropredatory vertebrate hunter living in shallow waters. It contains a single species, Kyhytysuka sachicarum.

References

  1. 1 2 Muller, Johannes (2005). "The Anatomy of Askeptosaurus italicus from the Middle Triassic of Monte San Giorgio and the Interrelationships of Thalattosaurs (Reptilia, Diapsida)". Canadian Journal of Earth Sciences. 42 (7): 1347–1367. Bibcode:2005CaJES..42.1347M. doi:10.1139/e05-030.
  2. ↑ Lawrence H. Tanner (2018). The Late Triassic World: Earth in a Time of Transition. Springer Nature. p. 291. ISBN   978-3-319-68008-8 . Retrieved 12 September 2022.
  3. ↑ Muller, Johannes (2007). "First Record of a Thalattosaur from the Upper Triassic of Austria". Journal of Vertebrate Paleontology. 27 (1): 236–240. doi:10.1671/0272-4634(2007)27[236:froatf]2.0.co;2.
  4. 1 2 Merriam, John C. (1904). A New Marine Reptile from the Triassic of California. Berkeley, CA: University of California Press.
  5. 1 2 Hilton, Richard (2003). Dinosaurs and Other Mesozoic Reptiles of California . California: University of California Press. pp.  80–82. ISBN   9780520233157.
  6. ↑ Williams, Rianna M (1994). Annie Montague Alexander: explorer, naturalist, philanthropist.
  7. ↑ Rieppel, Olivier; Nuller, Johannes; Liu, Jun (2005). "Rostral Structure in Thalattosauria (reptilia, Diapsida)". Canadian Journal of Earth Sciences. 42 (12): 2081–2086. Bibcode:2005CaJES..42.2081R. doi:10.1139/e05-076.
  8. 1 2 3 4 Merriam, John Campbell (1905). The Thalattosauria: a group of marine reptiles from the Triassic of California. The Academy.
  9. ↑ Nicholls, Elizabeth L.; Brinkman, Donald (1993). "New Thalattosaurs (reptilia: Diapsida) from the Triassic Sulphur Mountain Formationi of Wapiti Lake, British Columbia". Journal of Paleontology. 67 (2): 263–278. Bibcode:1993JPal...67..263N. doi:10.1017/S0022336000032194.
  10. 1 2 3 4 5 Nicholls, Elizabeth L. (1999). A Reexamination of Thalattosaurus and Nectosaurus and the Relationships of the Thalattosauria (reptilia: Diapsida). Berkeley, CA: University of California, Museum of Paleontology.
  11. ↑ Rieppel, Olivier; Liu, Johannes; Bucher, H (2000). "The First Record of a Thalattosaur Reptile from the Late Triassic of Southern China (Guizhou Provence, PR China)". Journal of Vertebrate Paleontology. 20 (3): 507–514. doi:10.1671/0272-4634(2000)020[0507:tfroat]2.0.co;2.
  12. ↑ "Thalattosauria". www.paleos.com.
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