squamosal horns. 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. An isolated quadratojugal was tentatively assigned to Shanxia and shares similar features to Euoplocephalus. The quadratojugal was described as sub-triangular in shape and generally similar to the quadratojugal horns of other ankylosaurids. Upchurch and Barrett, 2000 established two more additional distinguishing characteristics of Shanxia that differentiate it from other ankylosaurids, including Saichania, which include the absence of a large processus medialis humeri and a pair of large domed sub-rectangular osteoderms on the skull. However, similar ossifications are present in Tianzhenosaurus. 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. Barrett et al., 1998 noted that the holotype specimen preserves a possible synapomorphy with nodosaurids, the hemispherical occipital condyle is oval to subcircular in posterior view and offset from the braincase by a distinct 'neck'. 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 for Ankylosauria as the feature is also present in Tarchia, Talarurus, and Maleevus. Classification Barrett et al. (1998) originally considered Shanxia as an ankylosaurid with unknown affiliations, but Sullivan (1999) considered Shanxia as a nomen dubium, and possibly synonymous with the ankylosaurid Tianzhenosaurus, arguing that the unique shape of the squamosal horns could be a product of individual variation. However, Upchurch and Barrett (2000) reaffirmed the validity of Shanxia and recognised two new distinguishing characteristics. Thompson et al. (2012) recovered Shanxia as an ankylosaurine, sister taxon to “Crichtonsaurus” benxiensis and more basal than Tianzhenosaurus, while Arbour and Currie (2015) recovered Shanxia as a junior synonym of Tianzhenosaurus. A 2018 study by Wiersma and Irmis considered Shanxia as a valid taxon, and sister taxon to Tarchia kielanae and Minotaurasaurus ramachandrani. A phylogenetic analysis conducted by Thompson et al., 2012 is reproduced below. Paleoenvironment The holotype specimen of Shanxia was recovered from the Huiquanpu Formation, which possibly dates to the Cenomanian or Campanian stage of the Late Cretaceous. Due to the absence of index fossils, a precise dating is problematic. The proposed Cretaceous date is based in part on the discovery of pliosaur fossils. The