| Laosuchus Temporal range: Late Permian-Early Triassic, | |
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| Life restoration of Laosuchus naga | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | † Chroniosuchia |
| Genus: | † Laosuchus Arbez, Sidor & Steyer, 2018 |
| Type species | |
| Laosuchus naga Arbez, Sidor & Steyer, 2018 | |
| Other species | |
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Laosuchus is an extinct genus of chroniosuchian known from the Permian-Triassic boundary of Asia. Two species have been named.
L. naga was found in the Luang Prabang Basin of Northern Laos, part of the Indochina block. The site was first discovered by J. B. H. Counillon in 1896 as part of the Pavie's third Mission. Counillon was tasked with mapping mineral resources for the French colonial empire. L. naga was discovered during a 2005 expedition to the area, along with remains of dicynodonts. [1] [2] It was later described by Arbez, Sidor, and Steyer in 2018. [3] Its name comes from the Nāga, a snake-like deity that appears in multiple east Asian religions. In 2021 a new species L. hun was described from the Naobaogou Formation of the Daqing Mountains of Inner Mongolia, China. [4]
Laosuchus naga is represented by a single skull and articulated left hemimandible designated as specimen MDS-LPQ 2005-09, stored at the Musée des Dinosaures in Savannakhet. The skull, roughly 26 centimeters in length, is similar in shape to that of crocodiles. Its long snout bore marginal labyrinthodont teeth with an average height of 9 millimeters. Its nares are similar in shape to Madygenerpeton pustulatus. Like M. pustulatus, it also has oval-shaped orbits that are raised above the skull roof, but the orbits are proportionally smaller. Its choanae are relatively long compared to other chroniosuchians. [3]
L. naga has a number of traits that make it unique among chroniosuchia. It lacks palatal tusks, bearing only small denticles on the palate. Its pineal foramen is significantly reduced with a 1mm diameter(M. pustulatus, C. dongusensis, and B. schumanni have diameters of 2mm, 2.5mm, and 3.5mm respectively [5] [6] [7] ). A transverse flange extends from the pterygoid, contacting the maxilla. CT-scanning revealed an autapomorphic internal crest on the dorsal palate that follows the internal margin of the choanae. The parasphenoid bears a thin ventro-medial ridge, a condition also seen in Discosauriscus austriacus [8] Its tabular horn and posterior squamosal contact, closing the otic notch. [3]
There are a number of traits that L. naga share with other chroniosuchians. It bears a subtriangular fontanelle on its premaxilla, a poorly ossified braincase, a well developed pterygoid flange, and a relatively narrow parasphenoid bearing a crest between the basicranial joint. [3]
CT-scanning also revealed the presence of canals within the mandible, snout, and bones in front of the orbit. The canals in the skull roof are interpreted as being related to a lateral line system. Canals in the tip of the snout and mandible are more complex and could be neurovascular canals, which modern animals use for thermoreception, electroreception, or mechanoreception. The paleontologists who described L. naga suggest that the lateral line system was used to detect prey beneath the water surface while the neurovascular system could let it detect movement at the water surface similar to modern crocodiles. [3]
L. hun is distinguished from L. naga by several traits, including reduced palatal dentition, with a few denticles present on the vomer and pterygoid bones, and an irregular posterior cheek margin. [4]
The two families within chroniosuchia, Chroniosuchidae and Bystrowianidae, are differentiated primarily based on postcranial elements, such as the shape of their vertebrae and the degree of overlap between their dorsal osteoderms. [9] [10] Thus, while L. naga has numerous characteristics supporting its inclusion to chroniosuchia, the lack of postcranial elements in addition to several cranial traits preclude their inclusion to either family. As a result, L. naga was classified as Chroniosuchia incertae sedis . [3] In the 2021 description of L. hun postcranial remains indicated that Laosuchus belonged to the Chroniosuchidae. [4]
The depositional environment that L. naga occurred in consisted of braided rivers transitioning into alluvial plains, with an input of volcanic sediment. [2] In addition to this, the presence of a lateral line system and poorly ossified braincase imply that L. naga spent much of its time in the water. According to the paleontologists who described L. naga, Its placement in nonmarine sediment provides a line of support for the scenario that the North China Block, South China Block, and Indochina block were connected like a peninsula and linked to Laurussia during the Permian and Triassic. [11]
Temnospondyli or temnospondyls is a diverse ancient order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent. A few species continued into the Jurassic and Early Cretaceous periods, but all had gone extinct by the Late Cretaceous. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including freshwater, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are amphibians, many had characteristics such as scales and large armour-like bony plates (osteoderms) that generally distinguish them from the modern soft-bodied lissamphibians.
The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecological niche to modern crocodilians prior to the diversification of pseudosuchian archosaurs.
Euchambersia is an extinct genus of therocephalian therapsids that lived during the Late Permian in what is now South Africa and China. The genus contains two species. The type species E. mirabilis was named by paleontologist Robert Broom in 1931 from a skull missing the lower jaw. A second skull, belonging to a probably immature individual, was later described. In 2022, a second species, E. liuyudongi, was named by Jun Liu and Fernando Abdala from a well-preserved skull. It is a member of the family Akidnognathidae, which historically has also been referred by as the synonymous Euchambersiidae.
Chroniosuchidae is a family of semi-aquatic tetrapods found in sediments from the upper Permian and the upper Triassic periods, most in Russia. They were generally rather large animals, with long jaws similar to those found in modern crocodiles, and probably lived a similar lifestyle as riverside piscivores and ambush predators. Like all chroniosuchians, they bore extensive osteoderm armour on their backs, possibly as protection against terrestrial predators such as the Permian therapsids and the Triassic rauisuchians.
Chroniosuchus is an extinct genus of chroniosuchid from the upper Permian period. The genus was first named by Vjuschkov in 1957.
Chroniosaurus is an extinct genus of chroniosuchid stegocephalian, often considered a reptiliomorph but possibly a stem-tetrapod, from upper Permian deposits of Novgorod, Orenburg and Vologda Regions, Russia. It was first named by Tverdokhlebova in 1972 and the type species is Chroniosaurus dongusensis.
Bystrowiana is an extinct genus of bystrowianid chroniosuchian from upper Permian deposits of Vladimir Region, Russia and Jiyuan, China. Chroniosuchians are often thought to be reptiliomorphs, but some recent phylogenetic analyses suggest instead that they are stem-tetrapods. The genus is named in honour of the Russian paleontologist Alexey Bystrow. It was first described by Vyushkov in 1957 and the type species is Bystrowiana permira. Two species—B. permira and B. sinica—are known.
Saharastega is an extinct genus of basal temnospondyl which lived during the Late Permian period, around 251 to 260 million years ago. Remains of Saharastega, discovered by paleontologist Christian Sidor at the Moradi Formation in Niger, were described briefly in 2005 and more comprehensively in 2006. The description is based on a skull lacking the lower jaws.
Mastodonsauridae is a family of capitosauroid temnospondyls. Fossils belonging to this family have been found in North America, Greenland, Europe, Asia, and Australia. The family Capitosauridae is synonymous with Mastodonsauridae.
Chroniosuchia is a group of tetrapods that lived from the Middle Permian to Late Triassic in what is now Eastern Europe, Kyrgyzstan, China and Germany. Chroniosuchians are often thought to be reptiliomorphs, but some recent phylogenetic analyses suggest instead that they are stem-tetrapods. They were all rather short limbed with a strong tail and elongated snout, somewhat resembling modern crocodiles. The group is traditionally considered to be a suborder or order of labyrinthodonts. Chroniosuchians likely had ecological niches as riverside predators, and may have been outcompeted by semiaquatic true reptiles such as phytosaurs in the late Triassic. Most forms bore a heavy armour of scutes along the back, possibly for protection against land born predators like therapsids, or to strengthen the axial skeleton for terrestrial locomotion. Indeed, femoral microanatomy of Chroniosaurus suggests that it was amphibious to terrestrial.
Lapillopsis is an extinct genus of stereospondyl temnospondyl within the family Lapillopsidae. Fossils belonging to the genus have been found in the Arcadia Formation of Queensland, Australia.
Christian Alfred Sidor is an American vertebrate paleontologist. He is currently a Professor in the Department of Biology, University of Washington in Seattle, as well as Curator of Vertebrate Paleontology and Associate Director for Research and Collections at the Burke Museum of Natural History and Culture. His research focuses on Permian and Triassic tetrapod evolution, especially on therapsids.
Bystrowiella is an extinct genus of bystrowianid chroniosuchians from upper Middle Triassic deposits of Kupferzell and Vellberg, northern Baden-Württemberg, Germany.
Pneumatostega is an extinct genus of rhytidosteid temnospondyl from the early Triassic period of Cape Province of South Africa. It is known from the holotype BPI F981, a dorsal mould of a skull roof and from the referred specimen SAM 11188, partial skull fragments and postcranial remains recovered from the Lystrosaurus Assemblage Zone in the Beaufort Group near Middelburg. This genus was named by J. W. Cosgriff and J. M. Zawiskie in 1979, and the type species is Pneumatostega potamia.
Bystrowianidae is a family of chroniosuchian tetrapods from the Permian and Triassic periods.
Counillonia is an extinct genus of dicynodont therapsid from the area of Luang Prabang in Laos, Southeast Asia that lived at around the time of the Permian-Triassic boundary and possibly dates to the earliest Early Triassic. Its type and only known species is C. superoculis. Counillonia was related to the Triassic dicynodonts such as Lystrosaurus and the Kannemeyeriiformes that survived the Permian mass extinction, but it was more closely related to the Permian genus Dicynodon than to either of these lineages. Counillonia may then possibly represent another line of dicynodonts that survived the Permian mass extinction into the Triassic period, depending on its age. The discovery of Counillonia in Laos and its unexpected evolutionary relationships hint at the less well understood geographies of dicynodont diversity across the Permo-Triassic boundary outside of well explored regions like the Karoo Basin in South Africa.
Repelinosaurus is an extinct genus of dicynodont from the Purple Claystone Formation of Luang Prabang in Laos, Southeast Asia that lived at around the time of the Permian-Triassic boundary and possibly dates to the earliest Early Triassic. Its type and only known species is R. robustus. Repelinosaurus was originally described as the earliest known kannemeyeriiform dicynodont, supporting the idea of a more rapid radiation of the Triassic kannemeyeriiform dicynodonts during the Early Triassic following the Permian mass extinction. However, it may alternatively be more closely related to the Permian Dicynodon. The discovery of a potential early kannemeyeriiform in an understudied locality like Laos highlights the importance of such places in dicynodont research, which has been largely focused on historically important localities such as the Karoo Basin of South Africa.
The Naobaogou Formation is a geological formation in the Daqing Mountains of China. It is likely of Lopingian age. It consists of three rhythms of sediment, labelled members I-III primarily of purple siltstone, but each with a thick basal conglomerate bed. It is notable for its fossil content, producing one of the most diverse Late Permian vertebrate faunas outside Russia and South Africa.
This list of fossil amphibians described in 2018 is a list of new taxa of fossil amphibians that were described during the year 2018, as well as other significant discoveries and events related to amphibian paleontology that occurred in 2018.
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