| Shanxia | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Thyreophora |
| Clade: | †Ankylosauria |
| Family: | †Ankylosauridae |
| Subfamily: | †Ankylosaurinae |
| Genus: | †Shanxia Barrettet al.,1998 |
| Species: | †S. tianzhenensis |
| Binomial name | |
| †Shanxia tianzhenensis Barrettet al., 1998 | |
Shanxia (named after theShanxi Province) is a monospecificgenus ofankylosauriddinosaur from the Shanxi Province that lived during theLate Cretaceous (Cenomanian-Campanian, ~99-71 Ma) in what is now theHuiquanpu Formation.[1]Shanxia may possibly represent ajunior synonym ofTianzhenosaurus, anankylosaurine also known from the Huiquanpu Formation ofChina.[2]
In 1993, Messrs. Lu and Li of the Hebei Geological Survey discovered a partial ankylosaurid skeleton at a locality in theShanxi Province and notified staff of theInstitute of Vertebrate Paleontology and Paleoanthropology, who collected the material later that year.[1] Theholotype specimen,IVPP V11276, consists of a braincase, occiput, skull roof, ?quadratojugal, axis vertebra, cervical vertebrae, dorsal vertebrae, caudal vertebrae, humerus, fragment of ?ilium, femora and an osteoderm.[1] The holotype skull is partially reconstructed with plaster to stabilise parts of the skull roof and to attach the skull roof to the braincase.[3] Upchurch & Barrett, 2000 noted that the skull had not been artificially widened or lengthened by excess plaster.[3] The specimen was specifically obtained from theHuiquanpu Formation and is currently housed at the Institute of Vertebrate Paleontology and Paleoanthropology,Beijing.[1]
The generic name,Shanxia, refers to the Shanxi Province which is where the holotype was recovered from.[1] The specific name,tianzhenensis, refers to the Tian Zhen County.[1]
In 1999, Sullivans consideredShanxia as anomen dubium and as a possible junior syonynm ofTianzhenosaurus.[2] Sullivan noted that the only diagnosable characteristic, the unique shape of the squamosal horn, ofShanxia is known to be variable within a single taxon such asEuoplocephalus.[2] Sullivan also noted that due to the presence of two ankylosaurids in the Huiquanpu Formation, they were likely to represent the same taxon.[2] However, Upchurch & Barrett, 2000 consideredShanxia as a valid taxon based on at least onautapomorphy or diagnostic trait.[3] Thompson et al., 2012 also recoveredShanxia as a valid taxon based on the caudal projection of the squamosal horns, form of cranial armour and haemal arch attachment.[4] Arbour & Currie, 2015 considered that there are no unique characteristics that distinguishShanxia fromTianzhenosaurus, andTianzhenosaurus fromSaichania, an ankylosaurid from theBarun Goyot andNemegt Formation.[5]
Due to the fragmentary nature of the holotype specimen, not much information is known about the exact size and appearance ofShanxia.[1]
Barrett et al., 1998 distinguishedShanxia from all other ankylosaurids based on the morphology of the squamosal horns.[1] It was noted that the squamosal horns were slender and elongate, inclined at an angle, having a narrow junction with the skull roof in occipital view, and shaped like isosceles triangles in dorsal view.[1] An isolated quadratojugal was tentatively assigned toShanxia and shares similar features toEuoplocephalus.[1] The quadratojugal was described as sub-triangular in shape and generally similar to the quadratojugal horns of other ankylosaurids.[1] Upchurch and Barrett, 2000 established two more additional distinguishing characteristics ofShanxia that differentiate it from other ankylosaurids, includingSaichania, which include the absence of a large processus medialis humeri and a pair of large domed sub-rectangular osteoderms on the skull.[3] However, similar ossifications are present inTianzhenosaurus.[3] The holotype specimen only preserves one osteoderm, which has been described as oval in outline, sub-triangular in cross-section, excavated ventrally and has a prominent dorsal keel.[1]
Barrett et al., 1998 noted that the holotype specimen preserves a possiblesynapomorphy withnodosaurids, the hemispherical occipital condyle is oval to subcircular in posterior view and offset from the braincase by a distinct 'neck'.[1] However, they did state that some caution is needed in the interpretation of the synapomorphy as the shape of the occipital condyle is not entirely clear and may be primitive forAnkylosauria as the feature is also present inTarchia,Talarurus, andMaleevus.[1]
Barrett et al. (1998) originally consideredShanxia as an ankylosaurid with unknown affiliations, but Sullivan (1999) consideredShanxia as a nomen dubium, and possibly synonymous with the ankylosauridTianzhenosaurus, arguing that the unique shape of the squamosal horns could be a product of individual variation.[1][2] However, Upchurch and Barrett (2000) reaffirmed the validity ofShanxia and recognised two new distinguishing characteristics.[3] Thompson et al. (2012) recoveredShanxia as an ankylosaurine, sister taxon to“Crichtonsaurus” benxiensis and more basal thanTianzhenosaurus, while Arbour and Currie (2015) recoveredShanxia as a junior synonym ofTianzhenosaurus.[4][5] A 2018 study by Wiersma and Irmis consideredShanxia as a valid taxon, and sister taxon toTarchia kielanae andMinotaurasaurus ramachandrani.[6]
A phylogenetic analysis conducted by Thompson et al., 2012 is reproduced below.[4]
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The holotype specimen ofShanxia was recovered from the Huiquanpu Formation, which possibly dates to theCenomanian orCampanian stage of theLate Cretaceous.[1] Due to the absence of index fossils, a precise dating is problematic. The proposed Cretaceous date is based in part on the discovery ofpliosaur fossils.[1] The formation represents a fluvial environment, with the upper part of the formation being extensively reworked by a number of early Tertiary volcanic intrusions.[1]Shanxia would have coexisted with thesauropodHuabeisaurus,[7] theornithopodDatonglong,[8] thetyrannosauroidJinbeisaurus[9] and the ankylosauridTianzhenosaurus.[10]
