Nectosaurus

Last updated

Nectosaurus
Temporal range: Late Triassic, 235.0–221.5  Ma
Thalattosauridae.jpg
Thalattosaurus alexandrae (left) and Nectosaurus halius (right) of Late Triassic California
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Neodiapsida
Order: Thalattosauria
Superfamily: Thalattosauroidea
Genus: Nectosaurus
Species:
N. halius
Binomial name
Nectosaurus halius
Merriam 1905

Nectosaurus is a genus of thalattosaur (marine diapsid reptiles) 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 (along with Thalattosaurus ). [1]

Contents

Discovery

Nectosaurus is known from fragmentary remains. The holotype, UCMP 9124, is an incomplete skeleton including vertebrae, a humerus, coracoid, ulna, radius, and partial skull and mandibles. [2]

Many isolated bones from other localities were referred to the genus by Merriam in 1908. In addition, a partial skull from the same locality, UCMP 9120, was referred to the genus as Nectosaurus sp. in 1905. This specimen is much larger than any specimen of Nectosaurus halius but is otherwise similar to several referred specimens. UCMP 9120 may represent an adult specimen, making the holotype a juvenile specimen, a hypothesis supported by the fact that the holotype has unfused dermal bones and incomplete ossification on certain long bones. [2]

Description

Known skull elements of Nectosaurus specimens. Nectosaurus skull.tif
Known skull elements of Nectosaurus specimens.

Based on the position of the vomers, the general shape of the premaxillae was inferred to be that of a dramatically downward hooking rostrum, descending at a vertical angle. This trait is also known in Hescheleria as well as a specimen referred to Paralonectes in 1993. [3] Nectosaurus also had pointed, needle-like teeth (particularly in the front of the maxilla) and a mandible with a very high and pointed coronoid process. Like other thalattosauroids, the vomers and pterygoid also had teeth. [2]

Classification

Nectosaurus was a member of a group of marine reptiles known as thalattosaurs, characterized by their long, paddle-like tails and short legs with independently movable digits. Most thalattosaurs had extended premaxillae, forming a rostrum. Thalattosaurs with downward curving, hook-like premaxillae (such as Nectosaurus) are known as thalattosauroids. [3]

Although a 2001 analysis considered it a close relative of Xinpusaurus and Paralonectes because it was interpreted as having an upward-curving maxilla, further inquiry has shown that this was mistaken. [3]

Related Research Articles

<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.

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

Globidens is an extinct genus of mosasaur lizard classified as part of the Globidensini tribe in the Mosasaurinae subfamily.

<i>Batrachotomus</i> Genus of reptiles

Batrachotomus is a genus of prehistoric archosaur. Fossils of this animal have been found in southern Germany and dated from the Ladinian stage of the Middle Triassic period, around 242 to 237 million years ago. Batrachotomus was described by palaeontologist David J. Gower 22 years after its discovery.

Thalattosauria Extinct order of sea reptiles

Thalattosauria is an extinct order of prehistoric marine reptiles that lived in the middle to late Triassic period. 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.

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

Thalattosaurus 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 metres (6.6 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. It has gained notoriety as a result of studies on general diapsid phylogeny.

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

Acerosodontosaurus is an extinct genus of neodiapsid reptiles that lived during the Upper Permian of Madagascar. The only species of Acerosodontosaurus, A. piveteaui, is known from a natural mold of a single partial skeleton including a crushed skull and part of the body and limbs. The fossil was discovered in marine deposits of the Lower Sakamena Formation. In conjunction with several skeletal characteristics, this may indicate that Acerosodontosaurus individuals were at least partially aquatic.

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

Labidosaurikos is a genus of extinct captorhinid anapsid reptile that lived around 279 to 272 million years ago during Kungurian age of the lower Permian. The American Paleontologist John Willis Stovall first described Labidosaurikos in 1950, naming it "Labidosaurus like" for the striking similarity of the holotype skull of his specimen to the cranial anatomy of another captorhinid Labidosaurus hamatus. Labidosaurus or generally called "lipped lizard" is another genus of the family Captorhinidae whose name is derived from the Greek "forceps lizard" based on τσιμπίδα and σαυρος ("lizard")

<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.

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

Yonghesuchus is an extinct genus of Late Triassic archosaur reptile. Remains have been found from the early Late Triassic Tongchuan Formation in Shanxi, China. It is named after Yonghe County, the county where fossils were found. Currently only one species, Y. sangbiensis, is known. The specific name refers to Sangbi Creek, as fossils were found in one of its banks.

<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.

Thalattosauroidea 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>Jesairosaurus</i> Extinct genus of reptiles

Jesairosaurus is an extinct genus of early archosauromorph reptile known from the Illizi Province of Algeria. It is known from a single species, Jesairosaurus lehmani. Although a potential relative of the long-necked tanystropheids, this lightly-built reptile could instead be characterized by its relatively short neck as well as various skull features.

<i>Ymeria</i> Extinct genus of tetrapods

Ymeria is an extinct genus of early stem tetrapod from the Devonian of Greenland. Of the two other genera of stem tetrapods from Greenland, Acanthostega and Ichthyostega, Ymeria is most closely related to Ichthyostega, though the single known specimen is smaller, the skull about 10 cm in length. A single interclavicle resembles that of Ichthyostega, an indication Ymeria may have resembled this genus in the post-cranial skeleton.

<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. xinyiensis, was described in 2016.

<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.

References

  1. Sepkoski, J.J. (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology 363: 1-560.
  2. 1 2 3 Nicholls, Elizabeth (1999). "A reexamination of Thalattosaurus and Nectosaurus and the relationships of the Thalattosauria (Reptilia: Diapsida)". PaleoBios.
  3. 1 2 3 "Rostral structure in Thalattosauria (Reptilia, Diapsida) (PDF Download Available)". ResearchGate. Retrieved 2017-09-23.