| Yuxisaurus | |
|---|---|
 | |
| Skeletal diagram excluding osteoderms | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Thyreophora |
| Genus: | †Yuxisaurus Yao et al.,2022 |
| Species: | †Y. kopchicki |
| Binomial name | |
| †Yuxisaurus kopchicki Yao et al., 2022 | |
Yuxisaurus (lit. 'Yuxi lizard') is anextinct genus of earlythyreophoran dinosaur from theEarly Jurassic (Sinemurian-Toarcian)Fengjiahe Formation of southwestern China. The genus contains asingle species,Yuxisaurus kopchicki, known from a partial skeleton and manyosteoderms.
The name "Yuxisaurus kopchicki" first appeared in abioRxiv preprint released in late 2021. In March 2022, Xi Yao and colleagues formallydescribed it as a new genus and species of early-diverging armored dinosaur. Theholotype specimen, CVEB 21701, consists of a partial skeleton including parts of the skull, several vertebrae, partial limb bones, and at least 120 osteoderms.[1]
Thegeneric name,Yuxisaurus, combines a reference to thetype locality inYuxi,Yunnan Province, China, with theGreek "sauros", meaning "lizard." Thespecific name,kopchicki, honors the biologistJohn J. Kopchick.[1]
In their 2022 description ofYuxisaurus, Yao and colleagues identified it as abasal member of theThyreophora. Depending on the phylogenetic dataset used to test its position, it was recovered as either the sister taxon to the GermanEmausaurus (in a clade sister toScelidosaurus +Ankylosauria) or diverging afterEmausaurus, but beforeScelidosaurus andeurypodans (ankylosaurs + stegosaurs). The discovery ofYuxisaurus definitively proves that thyreophorans were present in Asia during the Early Jurassic, as other potential records of Early Jurassic Asian thyreophorans,Bienosaurus andTatisaurus, are too fragmentary to yield a confident identification.[1]
Topology A: Norman dataset | Topology B: Maidment et al. dataset
|
In 2026, Agnolín and colleagues described several skeletal elements from theLate CretaceousAllen Formation of Argentina that they referred toPatagopelta cristata. While this species was initially described as anodosaurid ankylosaur in 2022,[2] later analyses and discussions preferredparankylosaurian affinities.[3] To test the relationships ofPatagopelta, Agnolín et al. added it to the phylogenetic matrix of Raven et al. (2023), a dataset designed to test the relationships of all armored dinosaurs,[4] which had not previously sampled parankylosaurs in detail. Using an updated version of this matrix, Agnolín et al. (2026) conducted their phylogenetic analysis under equal weighting (Topology A below) andimplied weighting (Topology B below). Both versions recoveredStegouros,Antarctopelta,Patagopelta,Kunbarrasaurus, andMinmi as parankylosaurs.[5]
Their implied weights analysis notably recoveredYuxisaurus as the earliest-diverging member of the Parankylosauria, a result that has poor statistical support but is based on at least two shared anatomical characters. These include the morphology of thecervical (neck) vertebrae and certain distinctive osteoderm morphologies. Both taxa have large osteoderms over the distal (toward the end)caudal (tail) vertebrae described as'pup-tent'-like in morphology, and the cervical half-rings in both bear keeled lateral osteoderms and spine-like distal osteoderms, all of which are fused at the base. This placement is also consistent with earlier discoveries of relatives of Cretaceous dinosaur taxa from the Southern Hemisphere in Jurassic/Early Cretaceous rocks in China. Both analyses recovered Parankylosauria outside of its traditional placement within Ankylosauria. Instead, it was placed as thesister taxon toEurypoda (ankylosaurs +stegosaurs) or in an unresolvedpolytomy with these clades andYuxisaurus. The authors argued that Parankylosauria should be regarded as a lineage distinct from Ankylosauria, in part due to manyplesiomorphic ('ancestral') traits in parankylosaur skeletons.[5]
| Topology A: Equal weights analysis | Topology B: Implied weights analysis
|
| |||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||
