Miodentosaurus

Last updated

Miodentosaurus
Temporal range: Late Triassic
~235.0–221.5  Ma
Miodentosaurus BW.jpg
Life restoration
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Thalattosauria
Family: Askeptosauridae
Genus: Miodentosaurus
Cheng et al., 2007
Type species
Miodentosaurus brevis
Cheng et al., 2007

Miodentosaurus is a genus of thalattosaurian (a type of extinct marine reptile) 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. [1]

Contents

Description

Miodentosaurus is a thalattosaur, a group of marine reptiles with long, paddle-like tails and short legs with independently movable digits. It was a large member of the group, with a complete specimen measuring 4.4 metres (14 ft) long. [2] Miodentosaurus is specifically an Askeptosauroid, a specific group of thalattosaurs with rather straight snouts. Despite being closely related to Askeptosaurus (a thalattosaur with a very long and toothy snout), Miodentosaurus had a quite short snout (shorter than the rest of the head) with only a few conical teeth on the premaxillae and dentaries. Although this snout configuration is not known in any other thalattosaurians, Miodentosaurus does share a number of other features with Askeptosauroids, such as having 10 neck vertebrae and a large pineal foramen. [3]

Apart from its unique cranial features, Miodentosaurus also has characteristically flat front claws and the two specimens known were both more than four meters long, making it one of the largest thalattosaurs known. [2]

History and specimens

The holotype of Miodentosaurus brevis, NMNS 004727 / F003960, is a well-preserved and fairly complete articulated skeleton. It was discovered in the Carnian-age Xiaowa Formation (or Wayao Member of the Falang Formation) of China, where other thalattosaurs as Anshunsaurus huangguoshuensis and Concavispina biseridens were found. The skull and mandibles were the first elements described in 2007, [1] while the postcranial skeleton was described in 2009. [3]

An even more complete specimen, ZMNH M8742, was described in 2010. This specimen is one of the most complete thalattosaur skeletons known and also depicts pelvic, metatarsal, and coracoid features different from those of the holotype, showing instances of individual variation within the genus. [2]

A 2023 study by Chai et al. suggested that Miodentosaurus may actually represent the same animal as the contemporary Wayaosaurus, which was named in 2007, based on similarities in the skull, dorsal vertebrae, and pubis. This would render Miodentosaurus a subjective junior synonym of that genus. They also speculated that it is possible the two represent distinct species within the same genus. [4]

Related Research Articles

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

Keichousaurus is an extinct genus of pachypleurosaurian marine reptile from the Chialingchiang and Falang Formations of China with two known species attributed to the genus: K. hui and K. yuananensis.

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

Thalattosauria is an extinct order of 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.

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

Helveticosaurus is an extinct genus of diapsid marine reptile known from the Middle Triassic of southern Switzerland. It contains a single species, Helveticosaurus zollingeri, known from the nearly complete holotype T 4352 collected at Cava Tre Fontane of Monte San Giorgio, an area well known for its rich record of marine life during the Middle Triassic.

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

Guizhouichthyosaurus is an extinct genus of ichthyosaur which is known primarily from the Xiaowa Formation of the lower Carnian stage of the Late Triassic in southwest China. The type species of this genus is Guizhouichthyosaurus tangae, of which multiple skeletons are known. It has been reassigned as a species of the genus Shastasaurus in the past, though it has since been considered distinct. The ichthyosaurs Cymbospondylus asiaticus, named in 2002, and Panjiangsaurus epicharis, named in 2003, are junior synonyms of G. tangae. The genus is also known from the Ladinian-aged Middle Triassic Zhuganpo Formation; additionally, the species "Callawayia" wollongangense may belong to Guizhouichthyosaurus.

The Guanling Formation is a Middle Triassic geologic formation in southwestern China.

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

Sinosaurosphargis is an extinct genus of basal marine saurosphargid reptile known from the Middle Triassic Guanling Formation of Yunnan and Guizhou Provinces, southwestern China. It contains a single species, Sinosaurosphargis yunguiensis.

<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.

Diandongosaurus is an extinct genus of eosauropterygian known from the lower Middle Triassic of Yunnan Province, southwestern China. It is known from the holotype IVPP V 17761, a complete and articulated skeleton with skull, which was found in the middle Triassic Lagerstätte of the Guanling Formation. It was first named by Qing-Hua Shang, Xiao-Chun Wu, Chun Li in 2011 and the type species is Diandongosaurus acutidentatus. A referred specimen suggests a total body length of 34 cm (13 in).

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

Yunguisaurus is an extinct genus of pistosaur known from the Guizhou Province of China.

Qianxisaurus is an extinct genus of pachypleurosaur or alternatively a basal eosauropterygian known from the Middle Triassic of Guizhou Province, southwestern China. It contains a single species, Qianxisaurus chajiangensis.

<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.

The Ermaying Formation is a geological formation of Anisian age in north-central China. It is found across much of the Ordos Basin, at outcrops within the provinces of Shaanxi, Shanxi, and Inner Mongolia. It is composed of up to 600 m thick sequence of mudstone and sandstone, overlying the Heshanggou Formation and underlying the Tongchuan Formation. In the southern part of the Ordos Basin, the Zhifang Formation is equivalent to the Ermaying Formation.

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

Saurosphargidae is an extinct family of marine reptiles known from the Early Triassic and early Middle Triassic of Europe and China.

The Xiaowa Formation is a Carnian-age geological formation found in southern China. It is a sequence of limestone and marls from the Carnian stage of the Triassic. Its lower section was previously known as the Wayao Formation or Wayao Member of the Falang Formation. In 2002, the Wayao Member was renamed and raised to the Xiaowa Formation to prevent confusion with an Eocene unit of the same name. Crinoids and marine reptiles are abundant in the Xiaowa Formation, forming a lagerstätte known as the Guanling biota. Ammonoids and conodonts found in the formation constrain its age to the early Carnian. Reptiles of the Guanling biota include ichthyosaurs, thalattosaurs, placodonts, and Odontochelys. Sedimentary events within this formation have been tied to the Carnian Pluvial Event.

The Zhuganpo Formation is a Triassic geologic unit found in southern China. It has historically been known as the Zhuganpo Member of the Falang Formation. A diverse fossil assemblage known as the Xingyi biota or Xingyi Fauna can be found in the upper part of the Zhuganpo Formation. Fossils of the Xingyi biota include articulated skeletons of marine reptiles, abundant fish, and a plentiful assortment of invertebrates indicating a Ladinian to Carnian age for the sediments of the formation.

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

Dawazisaurus is an extinct genus of sauropterygian of possible nothosauroid affinities from the Middle Triassic Guanling Formation in China. The type species is D. brevis.

References

  1. 1 2 Cheng, Yen-Nien; Wu, Xiao-Chun; Sato, Tamaki (2007). "A new Thalattosaurian (Reptilia: Diapsida) From the Upper Triassic of Guizhou, China". Vertebrata PalAsiatica. 45 (3): 246–260.
  2. 1 2 3 Zhao, Li-Jun; Sato, Tamaki; Liu, Jun; Li, Chun; Wu, Xiao-Chun (2010). "A new skeleton of Miodentosaurus brevis (Diapsida: Thallatosauria) with a further study of the taxon" (PDF). Vertebrata PalAsiatica. 48 (1): 1–10.
  3. 1 2 Wu, Xiao-Chun; Cheng, Yen-Nien; Sato, Tamaki; Shan, Hsi-Yin (2009). "Miodentosaurus brevis Cheng et al. 2007 (Diapsida: Thalattosauria): Its postcranial skeleton and phylogenetic relationships". Vertebrata PalAsiatica. 47 (1): 1–20.
  4. Chai, Jun; Lu, Hao; Jiang, Da-Yong; Motani, Ryosuke; Druckenmiller, Patrick S.; Tintori, Andrea; Kelley, Neil P. (2023-10-23). "Reidentification of Wayaosaurus bellus and the conservative trunk and tail shape of Thalattosauria". Historical Biology: 1–20. doi:10.1080/08912963.2023.2264886. ISSN   0891-2963. S2CID   264474151.