| Shansisuchus | |
|---|---|
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| Skeletal reconstruction based on several specimens | |
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| Skull diagram | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Family: | †Erythrosuchidae |
| Genus: | †Shansisuchus Young,1964 |
| Type species | |
| †Shansisuchus shansisuchus Young, 1964 | |
| Species | |
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Shansisuchus (meaning "Shanxi Province crocodile") is an extinctgenus ofarchosauriform reptile belonging to the familyErythrosuchidae that lived during theMiddle Triassic in what is now China.[2][3] The first fossils ofShansisuchus were discovered from theErmaying Formation ofShanxi (Shansi) province in 1964 by Chinese paleontologistYang Zhongjian. Like other erythrosuchids,Shansisuchus was a large-bodied carnivore with a large, deep skull.[3]Shansisuchus is unique among early archosauriforms in having a hole in its skull called a subnarial fenestra.[4]
Shansisuchus is a large erythrosuchid distinguished from other members of the group by two characters: a tongue-and-groove articulation between thepremaxilla andnasal bones of the skull and the presence of a subnarial fenestra. InShansisuchus the premaxilla, a bone that makes up the front of the snout, projects backward and fits into a groove in the nasal, a bone that makes up the top of the snout. The subnarial fenestra is present between the external nares (nasal opening) and theantorbital fenestra, a hole in front of the eye socket. It is separated from the antorbital fenestra by a vertical projection of themaxilla bone. A subnarial fenestra is present in a few other morederived archosauriforms such as somedinosaurs andpseudosuchians, but its morphology inShansisuchus is unique.[5] The vertebrae are very short (with centra that are taller than long), and remarkably, one articulated specimen shows the presence of pretty developedintercentra throughout the entire vertebral column; which, instead of being in-between each vertebra as usual, these were positioned ventrally and wrapped around each articulation of the centra. These adaptations would have reduced flexibility, and made the neck very stiff and strong, likely in support of its relatively large head.[4]
Shansisuchus is known from many fossil skeletons representing more than a dozen individuals, making it one of the best known erythrosuchids. However, all but one specimen discovered in 2010 (a complete skull and 14 vertebrae fromJixian County) are disarticulated, meaning that many aspects of its anatomy had been poorly understood before that specimen was described. Several skeletal cast mounts have been made with parts of differently-sized specimens, with skulls inaccurately assembled from isolated bones glued in together with plaster.[2][4] Most specimens have been found in a fossil locality inWuxiang County, and others have been found in localities inNingwu,Yushe,Jingle, andXing counties. Three species ofShansisuchus have been named: thetype speciesShansisuchus shansisuchus, which is known from over ten individuals;S. heiyuekouensis, which is known from five individuals; andS. kuyeheensis, which is known from one individual.[4]
Shansisuchus belongs to a group of reptiles calledArchosauriformes, which is today represented bycrocodilians andbirds but also includes a diversity of extinct forms extending back to theLate Permian. It is abasal archosauriform that lies outsideArchosauria, thecrown group originating with thelast common ancestor of birds and crocodilians. WhenShansisuchus was first described, Yang placed it in its own family,Shansisuchidae. In 1992Shansisuchus was reassigned to the family Erythrosuchidae and proposed to be the closest relative of the genusVjushkovia (now considered a synonym ofGarjainia). Aphylogenetic analysis published in 2013 found thatVjushkovia was more closely related toErythrosuchus, and thatShansisuchus lied outside theVjushkovia+Erythrosuchusclade as a more basal erythrosuchid. Below is acladogram from the 2013 analysis:[4]
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