A new early branching armored dinosaur from the Lower Jurassic of southwestern China

Abstract

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. This new 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 unrealised morphological diversity early in the clade's history.

Ornithischian dinosaurs in Southeast Asia: a review with palaeobiogeographic implications

“…A few basal thyreophorans have been reported from Yunnan Province, China (Norman et al 2007;Yao et al 2022). During this epoch, basal thyreophorans are known from Africa, Europe and North America (Barrett et al 2014).…”

A new Cretaceous thyreophoran from Patagonia supports a South American lineage of armoured dinosaurs

“…The Early Jurassic thyreophoran record consists of basal forms known from several continents showing a Pangean distribution. These comprise Scutellosaurus (Hettangian-Toarcian of the USA 9 ), Scelidosaurus (Sinemurian of the UK; see 6,10 ), Emausaurus (Toarcian of Germany 42 ), 'Lusitanosaurus' (Sinemurian of Portugal 1 ), 'Bienosaurus' , 'Tatisaurus' (both from the Hettangian-Sinemurian of China; see 55,56 ) and Yuxisaurus (late Sinemurian-Toarcian 64 ). Some recent papers recover the unarmoured ornithischians Lesothosaurus (Hettangian-Sinemurian of South Africa and Lesotho; see 3,31 ) and Laquintasaura (Hettangian of Venezuela; see 3,4,65 ) as Gondwanan basal members of Thyreophora.…”