| Laosuchus | |
|---|---|
 | |
| Life restoration ofLaosuchus naga | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | †Chroniosuchia |
| Genus: | †Laosuchus Arbez, Sidor & Steyer, 2018 |
| Type species | |
| Laosuchus naga Arbez, Sidor & Steyer, 2018 | |
| Other species | |
| |
Laosuchus is an extinct genus ofchroniosuchian known from thePermian-Triassic boundary of Asia. Two species have been named.
L. naga was found in the Luang Prabang Basin of NorthernLaos, part of theIndochina block. The site was first discovered by J. B. H. Counillon in 1896 as part of thePavie'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 ofdicynodonts.[1][2] It was later described by Arbez, Sidor, and Steyer in 2018.[3] Its name comes from theNāga, a snake-like deity that appears in multiple east Asian religions. In 2021 a new speciesL. hun was described from theNaobaogou Formation of theDaqing Mountains ofInner 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 inSavannakhet. The skull, roughly 26 centimeters in length, is similar in shape to that of crocodiles. Its long snout bore marginallabyrinthodont teeth with an average height of 9 millimeters. Its nares are similar in shape toMadygenerpeton pustulatus. LikeM. 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, andB. 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 inDiscosauriscus austriacus[8] Its tabular horn and posterior squamosal contact, closing the otic notch.[3]
There are a number of traits thatL. 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 alateral 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, ormechanoreception. The paleontologists who describedL. 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 fromL. naga by several traits, including reducedpalatal dentition, with a few denticles present on thevomer andpterygoid bones, and an irregular posterior cheek margin.[4]
The two families within chroniosuchia,Chroniosuchidae andBystrowianidae, are differentiated primarily based on postcranial elements, such as the shape of their vertebrae and the degree of overlap between their dorsalosteoderms.[9][10] Thus, whileL. 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 Chroniosuchiaincertae sedis.[3] In the 2021 description ofL. hun postcranial remains indicated thatLaosuchus belonged to the Chroniosuchidae.[4]
The depositional environment thatL. 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 thatL. naga spent much of its time in the water. According to the paleontologists who describedL. naga, Its placement in nonmarine sediment provides a line of support for the scenario that theNorth China Block,South China Block, and Indochina block were connected like a peninsula and linked toLaurussia during the Permian and Triassic.[11]
