Open Paleo

Huayangosaurus

Dong et al., 1982 HWAH-YAHNG-o-SAWR-us

From Huayang (華陽), an alternate historical name for Sichuan Province, China, combined with Greek sauros (lizard); meaning 'Huayang lizard'

170.9–154.8 million years ago Bajocian–Oxfordian, Middle Jurassic–Late Jurassic
Middle Jurassic and Late Jurassic stages

Huayangosaurus is a genus of stegosaurian dinosaur from the Middle Jurassic of China. The name derives from "Huayang" (華陽), an alternate name for Sichuan (the province where it was discovered), and "saurus", meaning "lizard". It lived during the Bathonian to Callovian stages, around 165 million years ago, some 20 million years before its famous relative, Stegosaurus appeared in North America. At only approximately 4 meters (13 ft) long, it was also much smaller than its famous cousin. Found in the Lower Shaximiao Formation, Huayangosaurus shared the local Middle Jurassic landscape with the sauropods Shunosaurus, Datousaurus, Omeisaurus and Protognathosaurus, the ornithopod Xiaosaurus and the carnivorous Gasosaurus.

Under dispute

Huayangosaurus is an early-diverging stegosaur in the preferred analysis of each work read, though not always the earliest (Maidment and colleagues 2008). It is the type of Huayangosauridae, defined by Madzia and colleagues (2021) as all taxa closer to Huayangosaurus than to Stegosaurus, but the clade's content differs between analyses: Huayangosaurus and Chungkingosaurus only in the reference phylogeny of Madzia and colleagues (2021), five genera without Chungkingosaurus in most analyses of Sánchez-Fenollosa and Cobos (2025), and no such clade in Raven and colleagues (2023). Huayangosaurus is therefore placed at Stegosauria incertae sedis.

Diagnosis

  1. Premaxilla bears teeth, a primitive feature absent in all other known stegosaurs
  2. Small triangular antorbital fenestra anterior to the orbit
  3. Two supraorbital bones above the orbit
  4. Angular bone with a small mandibular foramen on its upper margin
  5. Four sacral vertebrae firmly fused; sacral centrum lacks pleurocoels; dorsal surface of sacrum not closed
  6. Cervical dermal ossicles rounded-oval; dorsal dermal ossicles narrow and spear-shaped

Species

Huayangosaurus taibaii Dong et al., 1982

Type species

Named for the great Tang Dynasty Chinese poet Li Bai, whose courtesy name was Taibai.

Holotype
IVPP V6728 , Institute of Vertebrate Paleontology and Paleoanthropology
Material
Composite skeleton including skull, incomplete vertebrae, girdles, and dermal plates
Horizon
lower Shaximiao Formation, Bajocian–Oxfordian, Middle Jurassic–Late Jurassic , 170.9–154.8 million years ago
Locality
Dashanpu Quarry, Sichuan, China

Notable specimens

  • ZDM T7001

    Zigong Dinosaur Museum complementary

    A referred skeleton more complete than the partial holotype, preserving anatomy the type lacks: a complete shoulder girdle, a humerus, both ilia, a pubic bone, both ischia, and eleven plates, substantially extending knowledge of the genus.

    Maidment et al. (2006)

References

  1. Dong, Z.; Tang, Z.; Zhou, S. W. (1982). Note on the new Mid-Jurassic stegosaur from Sichuan Basin, China. Vertebrata PalAsiatica 20(1): 83-87. dong1982a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026a
  3. Maidment, S. C. R.; Wei, G.; Norman, D. B. (2006). Re-description of the postcranial skeleton of the middle Jurassic stegosaur Huayangosaurus taibaii. Journal of Vertebrate Paleontology 26(4): 944-956. doi:10.1671/0272-4634(2006)26[944:ROTPSO]2.0.CO;2 maidment2006b
  4. Maidment, S. C. R.; Norman, D. B.; Barrett, P. M.; Upchurch, P. (2008). Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6(4): 367-407. Informa UK Limited. doi:10.1017/S1477201908002459

    Recovers Huayangosaurus among the earliest stegosaurs, with Gigantspinosaurus the most basal, and defines Huayangosauridae as stegosaurs closer to Huayangosaurus than to Stegosaurus.

    maidment2008a
  5. Madzia, D.; Arbour, V. M.; Boyd, C. A.; Farke, A. A.; Cruzado-Caballero, P.; Evans, D. C. (2021). The phylogenetic nomenclature of ornithischian dinosaurs. PeerJ 9: e12362. doi:10.7717/peerj.12362

    Registers Huayangosauridae as a defined clade, comprising Chungkingosaurus and Huayangosaurus under its reference phylogeny.

    madzia2021a
  6. Sánchez-Fenollosa, S.; Cobos, A. (2025). New insights into the phylogeny and skull evolution of stegosaurian dinosaurs: an extraordinary cranium from the European Late Jurassic (Dinosauria: Stegosauria). Vertebrate Zoology 75: 165-189. doi:10.3897/vz.75.e146618

    Divides Stegosauria into Huayangosauridae and Stegosauridae, with a five-genus Huayangosauridae that excludes Chungkingosaurus.

    sánchez-fenollosa2025a
  7. Raven, T. J.; Barrett, P. M.; Joyce, C. B.; Maidment, S. C. R. (2023). The phylogenetic relationships and evolutionary history of the armoured dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology 21(1): 2205433. doi:10.1080/14772019.2023.2205433

    In its preferred analysis finds Huayangosaurus an early stegosaur, sister to Isaberrysaura, with no Huayangosauridae; its equal-weights and Bayesian analyses place both outside Eurypoda.

    raven2023a