Scientists including Professor Paul Barrett of the London Natural History Museum have described a new species of basal armoured dinosaur from fossils found in China. The dinosaur named Yuxisaurus kopchicki, represents the first valid and undisputed member of the Thyreophora (armoured dinosaurs) to be described from fossils found in Lower Jurassic Asian strata.

A life reconstruction of the newly described, Early Jurassic Chinese armoured dinosaur Yuxisaurus kopchicki. Picture credit: Yu Chen.

Picture credit: Yu Chen

The Rapid Geographic Spread of Early Armoured Dinosaurs

With an estimated body length of around three metres, Yuxisaurus might be small compared to some of the later and much more famous members of the Thyreophora clade such as Ankylosaurus and Stegosaurus, but confirmation of the presence of early armoured dinosaurs in China underlines the rapid geographic dispersal of these ornithischians. The first armoured dinosaurs are thought to have evolved around 200 million years ago (Hettangian faunal stage of the Early Jurassic). Yuxisaurus fossils consisting of vertebrae, skull bones, elements from the limbs, shoulder blades (scapulae) and 120 osteoderms (bony armour), were excavated from the upper portion of Fengjiahe Formation exposures, near Jiaojiadian village, Yimen County, Yuxi Prefecture, Yunnan Province (southwestern China).

Although the dating of the strata has proved problematical, it is likely that the fossils are somewhere between 192 and 182 million years old (late Sinemurian to early Toarcian stage of the Early Jurassic).

Variety Amongst Early Members of the Thyreophora

Although relatively small compared to later armoured dinosaurs, the limb bones suggest a robust, stout animal indicating that Yuxisaurus had a different body shape compared to other known early thyreophorans such as Scutellosaurus and Emausaurus. This suggests that early armoured dinosaurs had a diverse morphology and ecology and they spread rapidly establishing a wide geographical distribution and filling a variety of niches in Early Jurassic ecosystems.

Skeletal reconstruction of Y. kopchicki showing main preserved elements from the holotype (highlighted in blue). Details of the skull bones (A), cervical vertebrae (B) and dorsal vertebrae (C). The left scapula is shown (D) and the right humerus (E) along with the distal portion of the left femur (F). Note scale bars equal 5 cm for A-C and 10 cm for D-F. Osteoderms have been omitted to show the skeleton. Picture credit: Xi Yao.

Picture credit: Xi Yao

The First Unambiguous Armoured Dinosaur from the Early Jurassic of Asia

First author of the scientific paper, Professor Paul Barrett (Natural History Museum, London), commented:

“Although we’ve had tantalising fragments of early armoured dinosaurs from Asia, this is the first time we’ve had enough material to recognise a new species from the region and investigate its evolutionary history. I hope it’s the first of many new dinosaurs from the localities being discovered by my colleagues in Yunnan.”

Senior author of the paper, Dr Shundong Bi, a professor at Indiana University of Pennsylvania, explained that the dinosaur had been named Yuxisaurus kopchicki in honour of the Yuxi Prefecture, whilst the trivial or species name was in recognition of the work of molecular biologist Dr John J. Kopchick and for his support and funding of a new Indiana University of Pennsylvania science complex which is due to open in autumn 2023.

Dr Shundong Bi stated, that despite its robust body:

“Yuxisaurus was possibly a facultative quadrupedal. It was primarily adapted for walking on four legs, but also able to walk on two legs.”

Where Did Armoured Dinosaurs Originate?

Until recently all the unambiguous Early Jurassic Thyreophora taxa were described from fossils found in North America (Scutellosaurus) or Europe (Emausaurus and Scelidosaurus). This led palaeontologists to conclude that armoured dinosaurs originated in Laurasia, however, new phylogenetic analyses (Butler et al 2020, Boyd 2015, Raven and Maidment 2017, Maidment et al 2020 and Baron et al 2017a) have proposed that Lesothosaurus from southern Africa and Laquintasaura from Venezuela might also represent early members of the Thyreophora. If Lesothosaurus and Laquintasaura are early armoured dinosaurs, then this suggests that this clade could have originated in Gondwana.

Phylogenetic assessments plotting the relationship of Yuxisaurus within the Thyreophora. Analysis (A) modified from Norman (2021) dataset which places Yuxisaurus as a sister taxon to Emausaurus which is known from the Early Jurassic (Toarcian) of Germany. Analysis (B) modified from Maidment et al (2020) places Yuxisaurus within the Thyreophora as an early-diverging branch between Emausaurus and Scelidosaurus which is known from the older sedimentary deposits from Charmouth on the Dorset coast. Picture credit: Yao et al.

Picture credit: Xi Yao et al

The phylogeny of early ornithischians remains disputed, it is hoped that further fossil finds will resolve this debate.

Everything Dinosaur acknowledges the assistance of a media release from the London Natural History Museum in the compilation of this article.

To read an article about the discovery of Laquintasaura: Laquintasaura What Does it All Mean?

The scientific paper: “A new early-branching armoured dinosaur from the Lower Jurassic of southwestern China” by Xi Yao, Paul M. Barrett, Lei Yang, Xing Xu and Shundong Bi preprint via bioRxiv before publication in eLife.

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The trouble with being regarded as the biggest, longest, tallest or oldest when you are newly described species of dinosaur, is that sooner or later another fossil discovery will take this claim away from you. Back in 2019, team members wrote a blog post about the discovery of Adratiklit boulahfa from the Middle Jurassic of Morocco North Africa’s First Stegosaur. The fossils of this armoured dinosaur were estimated to be around 168 million years old (Bathonian faunal stage), making Adratiklit the oldest definitive stegosaur described.

Scientists including Dr Susannah Maidment a senior researcher at the London Natural History Museum, who co-authored the paper describing A. boulahfa, have announced the discovery of an even older stegosaur, this time from China. The new stegosaur named Bashanosaurus primitivus is at least one million years older than the Moroccan stegosaur.

The Fossils of Bashanosaurus

The fossils of Bashanosaurus herald from the Lower Member of the Shaximiao Formation and radiometric dating based on isotope decay analysis using zircon crystals (geochronological data), suggest that the deposits associated with the fossil bones are around 169 ± 0.68 million years of age.

A life reconstruction of the newly described Chinese stegosaur Bashanosaurus primitivus. Picture credit: Banana Art Studio.

Picture credit: Banana Art Studio

Did the Stegosauria Evolve in Asia?

The fossil record of early stegosaurs is highly fragmentary and the evolution of this iconic branch of the Thyreophora is poorly understood. The Stegosauria represents a major clade within the Ornithischia (bird-hipped dinosaurs). Fourteen genera of stegosaur have been described to date and they are both geographically and temporally widespread, known from all the major landmasses except for Australia and Antarctica.

In 2016, a new dinosaur quarry was opened in Yunyang County, Chongqinq Municipality in southwestern China. Stegosaur fossil material was identified on the western side of the quarry. The disarticulated material preserved within the sandstone consisted of a dorsal vertebra, two tail bones (caudal vertebrae), a right scapula, a right coracoid and elements from the hind legs. Three pieces of dermal armour were also discovered at this location (one plate and two spines) along with fragments of rib bones. These fossils (CLGPR V00006-1) are regarded as the holotype of B. primitivus.

Potentially Three Bashanosaurus Specimens

More stegosaur fossils were found at the site approximately fifty metres away from the holotype material (CLGPR V00006-2). They consist of five dorsal vertebrae, a right tibia, a right fibula some ribs and a single piece of dermal armour (one plate). In addition, a single dorsal vertebra (CLGPR V00006-3) was found on the eastern part of the site some one hundred and twenty metres away from the holotype material.

Whilst the researchers have confidently assigned these fossils to the Stegosauria and specifically to Bashanosaurus primitivus, three individual stegosaurs are represented by the bones.

Photograph (A) with interpretative line drawing showing the position of the B. primitivus holotype fossil material (CLGPR V00006-1) on the western side of the wall of dinosaur fossils. Photograph (B) with interpretative line drawing showing the second location with B. primitivus fossil material ((CLGPR V00006-2) towards the middle of the wall of dinosaur fossils. Picture credit: Hui et al.

Picture credit: Hui et al

It is not known whether the fossil bones represent a juvenile or a fully-grown animal. However, based on these bones, the researchers estimate that the largest stegosaur from the quarry was about 2.8 metres in length.

Unique Anatomical Traits

The scientists who include researchers from the Chongqing Bureau of Geological and Mineral Resource Exploration and Development in China and London’s Natural History Museum identified several unique anatomical traits that led to the erection of a new genus. Bashanosaurus possesses anatomical characteristics associated with basal thyreophorans as well as more derived features associated with early stegosaurs. For example, it has a smaller and less developed shoulder blade, the bony projection of the thighbone (fourth trochanter) is positioned below the middle of the shaft and the bases of the armour plates curve outwards and are thicker than the plates on the backs of later stegosaurs.

The genus name is derived from “Bashan” in reference to the ancient name for the area of Chongqing in China where the dinosaur was found. The species moniker is derived from the Latin for “first” – primitivus.

Lead author of the research team, Dr Dai Hui from the Chongqing Bureau of Geological and Mineral Resource Exploration and Development commented:

“All these features are clues to the stegosaurs’ place on the dinosaur family tree. Bashanosaurus can be distinguished from other Middle Jurassic stegosaurs, and clearly represents a new species.”

Phylogenetic Analysis

Phylogenetic analysis shows that Bashanosaurus primitivus is the earliest-diverging stegosaur, along with Chungkingosaurus (C. jiangbeiensis), which is thought to be closely related, although Chungkingosaurus lived much later than Bashanosaurus. Chungkingosaurus fossils are known from the Upper Member of the Shaximiao Formation.

The discovery of Bashanosaurus will help researchers to learn more about the evolution of stegosaurs and supports the theory that this type of armoured dinosaur first appeared in Asia. Although there have been some exciting fossil discoveries helping to improve understanding with regards to the evolution of armoured dinosaurs (Thyreophora), there are still numerous gaps in the fossil record which makes mapping the evolutionary development of these iconic dinosaurs extremely difficult.

For example, Everything Dinosaur recently wrote an article about the discovery of the basal thyreophoran Yuxisaurus kopchicki, whose fossils also come from China. Scientists from the London Natural History Museum also contributed to the scientific paper on Yuxisaurus: The Earliest Armoured Dinosaur Found to Date.

Everything Dinosaur has inserted Yuxisaurus kopchicki within the phylogenetic assessment of Bashanosaurus to help put these recent fossil discoveries into context (see below).

A phylogenetic analysis showing the placement of B. primitivus within the Stegosauria. It is believed to be around one million years older than the recently described Adratiklit boulahfa (Maidment et al) from the Middle Jurassic of Morocco. The earliest armoured dinosaur from Asia known to date (Yuxisaurus kopchicki) from Yunnan Province, China (Yao et al) has been incorporated into the image by Everything Dinosaur to show the approximate phylogenetic and temporal placement of Y. kopchicki when compared to B. primitivus. Picture credit: Hui et al with additional annotation by Everything Dinosaur.

Picture credit: Hui et al with additional annotation by Everything Dinosaur

The Stegosauria Clade Originated in Asia?

Commenting on the phylogenetic assessment Dr Hui stated:

“What’s more, our analysis of the family tree indicates that it [B. primitivus] is one of the earliest-diverging stegosaurs along with the Chongqing Lizard (Chungkingosaurus) and Huayangosaurus. These were all unearthed from the Middle to Late Jurassic Shaximiao Formation in China, suggesting that stegosaurs might have originated in Asia”

An illustration of the Chinese Stegosaur Chungkingosaurus. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The picture (above) shows a drawing of a model from the PNSO model range.

To view this range of prehistoric animal figures: PNSO Age of Dinosaurs Figures.

Co-author of the scientific paper published in the Journal of Vertebrate Paleontology, Dr Susannah Maidment of the London Natural History Museum and an expert in ornithischian dinosaurs added:

“The discovery of this stegosaur from the Middle Jurassic of China adds to an increasing body of evidence that the group evolved in the early Middle Jurassic, or perhaps even in the Early Jurassic, and as such represent some of the earliest known bird-hipped dinosaurs. China seems to have been a hotspot for stegosaur diversity, with numerous species now known from the Middle Jurassic right the way through until the end of the Early Cretaceous period.”

Everything Dinosaur acknowledges the assistance of a media release from the Taylor & Francis Group in the compilation of this article.

The scientific paper: “New Stegosaurs from the Middle Jurassic Lower Member of the Shaximiao Formation of Chongqing, China” by Dai Hui, Li Ning, Susannah C. R. Maidment, Wei Guangbiao, Zhou Yuxuan, Hu Xufeng, Ma Qingyu, Wang Xunqian, Hu Haiqian and Peng Guangzhao published in the Journal of Vertebrate Paleontology.

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