Yuxisaurus

*Yuxisaurus kopchicki*

***Yuxisaurus*** is a genus of thyreophoran from the Lower Jurassic Fengjiahe Formation of Yunnan Province.

## Etymology

The generic name refers to the type locality in Yuxi Prefecture, with the suffix -saurus from the Greek, meaning reptile. The specific name is after Dr. John J. Kopchick in recognition of his contributions to biology and the IUP Science Building.

## Locality

Upper part of the Fengjiahe Formation, near Jiaojiadian village, Yimen County, Yuxi Prefecture, Yunnan Province, China; ?late Sinemurian–Toarcian.

## Description

*Yuxisaurus* is the first described thyreophoran from the Early Jurassic of Asia. This species confirms a rapid geographic spread and diversification of thyreophorans after the Hettangian. It is heavily-built, with distinct armour that morphologically separate from others.

It is a medium-sized armoured dinosaur that can be distinguished from all other thyreophorans by the following autapomorphies: deep, subtriangular, dorsoventrally elongated depression on either side of the nuchal crest; a ‘V’-shaped notch on the dorsal margin of the paroccipital process; basal tubera that are considerably ventrally offset with respect to the occipital condyle, so that they are clearly visible in posterior view; basipterygoid processes that are ventrally offset with respect to the basal tubera, creating a dorsoventrally deep, ‘stepped’ basicranial profile in lateral view; cultriform process ventrally offset with respect to the occipital condyle in lateral view; angular with elongate, dorsally deflected posterior process that almost reaches the posterior margin of the retroarticular process; atlas intercentrum with symmetrical anterolaterally directed low ridges and associated arrow-like depressions on its ventral surface; relatively short anterior cervical centra; cervical centra lack ventral keels.

This taxon, *Yuxisaurus kopchicki*, represents the first valid thyreophoran dinosaur to be described from the Early Jurassic of Asia and confirms the rapid geographic spread and diversification of the clade after its first appearance in the Hettangian. Its heavy build and distinctive armour also hint at previously unrealized morphological diversity early in the clade’s history.

In addition, *Yuxisaurus* can be distinguished from other early thyreophorans using the following combination of character states: antorbital fossa subtriangular in outline, unlike that of *Scelidosaurus*, and with rounded corners, unlike that in *Scutellosaurus*; anterior ramus of the jugal projects posteroventrally, rather than horizontally as in *Emausaurus*, *Scelidosaurus*and *Scutellosaurus*; maxillary tooth row bowed medially to a greater degree than in *Emausaurus*, *Scelidosaurus* or *Scutellosaurus*; maxillary tooth crowns bearing well-defined ridges, which are absent in *Emausaurus*, *Scelidosaurus* and *Scutellosaurus*; a relatively short axial neural spine with a sinuous dorsal margin in lateral view, contrasting with the straight margin and significant posterior expansion of the neural spine present in *Scelidosaurus*; elongate axial rib, which extends to the midpoint of cervical vertebra 3, unlike the shorter rib present in *Scelidosaurus*; absence of lateral ridge on the axial rib, which is present in *Scelidosaurus*; proximal and distal expansions of the humerus relatively larger than in *Scelidosaurus* and *Scutellosaurus*; deep notch separating the humeral head and dorsal margin of the internal tuberosity, which is absent in *Scelidosaurus* and *Scutellosaurus*; and broad, ‘U’-shaped fossa on anterior surface of distal humerus, contrasting with the narrow, ‘V’-shaped fossae in *Scelidosaurus* and *Scutellosaurus*.

The early evolutionary history of the armoured dinosaurs (Thyreophora) is obscured by their patchily distributed fossil record and by conflicting views on the relationships of Early Jurassic taxa. Here, we describe an early-diverging thyreophoran from the Lower Jurassic Fengjiahe Formation of Yunnan Province, China, on the basis of an associated partial skeleton that includes skull, axial, limb and armour elements. It can be diagnosed as a new taxon based on numerous cranial and postcranial autapomorphies and is further distinguished from all other thyreophorans by a unique combination of character states. Although the robust postcranium is similar to that of more deeply nested ankylosaurs and stegosaurs, phylogenetic analysis recovers it as either the sister taxon of *Emausaurus* or of the clade *Scelidosaurus*+Eurypoda.

## Appearance in other media

### *Jurassic Park*

* *Yuxisaurus* will make its first appearance in the game *Jurassic World: Alive* as an Omega dinosaur. The database entry mentions that it was discovered in 2021, when in reality, it was discovered in 2022. The good news is that this will be the first time a dinosaur from 2022 will appear in the franchise.

## References

* https://www.biorxiv.org/content/10.1101/2021.11.24.469951v1.full
* https://inews.co.uk/news/dinosaur-prickly-rhino-china-yuxisaurus-kopchiki-stegosaur-vegetarian-1517641
* https://elifesciences.org/articles/75248