''Bashanosaurus'' (meaning "Bashan lizard", after an ancient name for Chongqing) is a genus of

stegosaur Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Euro ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

recovered from the

Bajocian In the geologic timescale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relatin ...

(

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations ...

)-aged

Shaximiao Formation The Shaximiao Formation () is a Middle to Late Jurassic aged geological formation in Sichuan, China, most notable for the wealth of dinosaurs fossils that have been excavated from its strata. The Shaximiao Formation is exposed in and around the ...

of Yunyang,

Chongqing Chongqing ( or ; ; Sichuanese pronunciation: , Standard Mandarin pronunciation: ), alternately romanized as Chungking (), is a municipality in Southwest China. The official abbreviation of the city, "" (), was approved by the State Cou ...

, China. The type species is ''Bashanosaurus primitivus''. It is one of the basalmost stegosaurs and is also the oldest known stegosaur, supplanting the previous oldest known stegosaur, ''

Adratiklit ''Adratiklit'' (meaning "mountain lizard") is an extinct genus of herbivorous stegosaurian dinosaur that lived on the supercontinent Gondwana during the Middle Jurassic period (168–164 million years ago). The genus contains a single species, '' ...

'', which is roughly one million years younger.

Discovery and naming

''Bashanosaurus'' is known from two partial skeletons, along with a vertebra that comes from a third individual; these remains were preserved on the Dinosaur Fossil Wall, preserved within the

Zigong Dinosaur Museum The Zigong Dinosaur Museum () is located near the city of Zigong, Sichuan, China, in the township of Dashanpu. History The museum sits on top of a large concentration of a diverse dinosaur assemblage from the Shaximiao Formation. The mus ...

, along the with another specimen, a partial cranium, a dorsal vertebra, and a piece of dermal armour (CLGPRChongqing Laboratory of Geoheritage Protection and Research V00006), which belongs to an unnamed indeterminate stegosaur. The material was recovered from a quarry in

discovered in 2016, hailing from the

. The specimens were given the name ''Bashanosaurus primitivus'' in a 2022 paper, in reference to the old name of Chongqing and its basal position. The holotype, CLGPR V00006-1, includes limb bones, back and tail vertebrae, plates and a spike. The second specimen CLGPR V00006-2, consists of five vertebrae, a right lower leg and a plate. The third specimen is CLGPR V00006-3, a back vertebra. A fourth specimen, CLGPR V00006-4, a partial skeleton with skull, was not referred as it does not share unique traits with the holotype.

Description

Its describers estimate the holotype to have been long, but given that the specimens are subadult, ''Bashanosaurus'' may have grown larger.

Classification

Several of its features are reminiscent of the basal thyreophoran '' Scelidosaurus'', although it also possesses plesiomorphic thyreophoran traits as well as traits more derived stegosaurs. In light of this unique mosaic of features, a phylogenetic analysis placed it as the most basal stegosaur, in a clade with ''

Chungkingosaurus ''Chungkingosaurus'', meaning "Chongqing Lizard", is a genus of herbivorous dinosaur from the Late Jurassic Upper Shaximiao Formation in what is now China. It is a member of the Stegosauria. Description According to Dong e.a. the ''Chungkingosa ...

'', consistent with its early age.

References

{{Thyreophora, S. Middle Jurassic dinosaurs of Asia Stegosaurs Fossil taxa described in 2022 Paleontology in China Ornithischian genera