Open Paleo

Omeisaurus

Young, 1939 UH-may-SAWR-us

Named after Mount Emei (Omei) in Sichuan Province, China, where it was discovered, combined with Greek 'sauros' (lizard); meaning 'Omei lizard'.

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

Omeisaurus is a genus of sauropod dinosaur from the Middle to Late Jurassic Period (Bathonian-Oxfordian stage) of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao Formation of Sichuan Province.

Diagnosis

  1. Processus pseudospinosus remarkably developed with straight upper border; 255 mm long wing on neck vertebrae
  2. Only 3 primary sacral vertebrae with strongly built sacral ribs and plate-like lamellae
  3. First caudal vertebra with broad transversal fan-like expansion of caudal rib
  4. Coracoid very short and distally rounded with straight scapula border, breadth exceeds length
  5. Femur head well differentiated with prominent fourth trochanter visible from anterior view
  6. Fibula with round shaft lacking ridge from proximal to distal end characteristic of other sauropods

Species (5)

Omeisaurus junghsiensis Young, 1939

Type species

Named for the Junghsi locality in Sichuan, China, where the holotype was collected.

Neotype
CV 001 , Chongqing Museum of Natural History
Material
Skull, the most complete cranial element recovered from the Wujiaba quarry
Notes
Young (1939) named the species on postcranial material from Junghsien that carried no catalog number and was mostly lost in transport during the Second World War. Dong and colleagues (1983) selected CV 001 as the neotype and CV 002 as paratype, both from the Wujiaba quarry at Zigong. IVPP V930, sometimes cited for this species, is the type of Omeisaurus changshouensis Young, 1958.
Horizon
upper Shaximiao Formation, Bajocian–Oxfordian, Middle Jurassic–Late Jurassic , 170.9–154.8 million years ago
Locality
Wujiaba Dam, Zigong, Sichuan, China

Omeisaurus tianfuensis He et al., 1984

Named for Tianfu (Land of Abundance), a traditional name for Sichuan, the region of the fossil locality.

Holotype
ZDM T5701 , Zigong Dinosaur Museum
Material
Nearly complete postcranial skeleton lacking the skull, 2-3 middle cervical vertebrae, posterior caudal vertebrae, and most fore and hind limb elements.
Horizon
lower Shaximiao Formation, Bajocian–Oxfordian, Middle Jurassic–Late Jurassic , 170.9–154.8 million years ago
Locality
Dashanpu, Zigong, Sichuan, China
Diagnosis
  1. Lateral (pleurocoel) depressions of the cervical and dorsal vertebrae more strongly developed than in O. junghsiensis
  2. First caudal rib narrower and less ventrally extended than the broader, more downward-extending first caudal rib of O. junghsiensis
  3. Pubis relatively longer and more slender than the shorter, stouter pubis of O. junghsiensis

Omeisaurus jiaoi Jiang et al., 2011

Honors Jiao Zheng of the Zigong Dinosaur Museum development group.

Holotype
ZDM 5050 , Zigong Dinosaur Museum
Material
Nearly complete postcranial skeleton lacking skull and cervical vertebrae: 12 dorsal vertebrae, 5 sacral vertebrae, 29 caudal vertebrae, partial dorsal ribs and chevrons, essentially complete pectoral girdle, pelvic girdle, and fore and hind limbs.
Horizon
lower Shaximiao Formation, Bajocian–Oxfordian, Middle Jurassic–Late Jurassic , 170.9–154.8 million years ago
Locality
Dashanpu, Zigong, Sichuan, China
Diagnosis
  1. First caudal vertebra lacks the fan-shaped caudal ribs seen in the Omeisaurus type species and O. tianfuensis; the rib is laterally directed with only slight anteroposterior expansion of the tip.
  2. Tail markedly shorter than in O. tianfuensis: length of the first 25 caudal vertebrae is only 121% of total dorsal length, versus 148% in O. tianfuensis.
  3. First chevron is very slender and articulates with the first caudal vertebra, unlike O. tianfuensis, in which the largest chevron articulates with the second caudal vertebra.
  4. Scapula is more slender with a more expanded distal end (maximum distal width about 2x minimum shaft width) than in O. tianfuensis (about 1.6x).
  5. Dorsal neural spine apices are not greatly expanded and anterior caudal vertebrae lack ventral keels, unlike O. luoquanensis, which also has lower, plate-like anterior caudal neural spines.

Omeisaurus puxiani Tan et al., 2021

Named for Samantabhadra (Pu Xian), Bodhisattva of Mount Emei; 'Pu' also references Pu'an, the type locality.

Holotype
CLGPR V00005 , Chongqing Laboratory of Geoheritage Protection and Research
Material
Partial articulated skeleton: 10 cervicals, 12 dorsals, partial sacrum, 24 caudals, rib/chevron fragments, partial clavicle, right forelimb, partial ilia, femora, right tibia and fibula
Horizon
lower Shaximiao Formation, Bajocian–Oxfordian, Middle Jurassic–Late Jurassic , 170.9–154.8 million years ago
Locality
Laojun Village, Pu'an Township, Yunyang County, Chongqing, China
Diagnosis
  1. Neural spines of posterior dorsal vertebrae are transversely extended, unlike the anteroposterior extension seen in other Omeisaurus species
  2. Distal ends of anterior caudal neural spines expand posteriorly with a bifid extension, a feature not seen in other Omeisaurus species
  3. Lateral fossae of dorsal centra are divided by secondary septa, more prominently developed than in congeners such as O. tianfuensis and O. jiaoi
  4. Edge of humerus deltopectoral crest turns posterolaterally, differing from the anterolateral orientation in O. tianfuensis
  5. Ratio of ulna length to humerus length is relatively high, at 0.69
  6. Highest cervical elongation index exceeds four (4.4 in cervical 9), among the highest recorded in the genus

Omeisaurus maoianus Tang et al., 2001

Named for Mao Zhaoxi, professor at Zhejiang University and former director of the Cultural Bureau of Zhejiang Province, who supported the work.

Holotype
ZMNH N8510 , Zhejiang Museum of Natural History
Material
A skull and mandible, with three cervical, four dorsal and 22 caudal vertebrae, the pelvic girdle and nearly complete limbs; the pectoral girdle is missing.
Horizon
upper Shaximiao Formation, Bajocian–Oxfordian, Middle Jurassic–Late Jurassic , 170.9–154.8 million years ago
Locality
Huangshikan (now Tongqian Village), about 8 km east of Yanjing Town, Jingyan County, Sichuan, China
Diagnosis
  1. Snout broad and bluntly rounded in dorsal view, with a slight step from the anterior margin of the premaxilla to its ascending ramus
  2. Posterior margin of the external naris behind the anterior margin of the antorbital fenestra, and no small foramen anteroventral to the antorbital fenestra
  3. Jugal articulating medially with a twisted, columnar ectopterygoid
  4. Supratemporal fenestra bordered by the parietal, postorbital and squamosal
  5. Twenty-three dentary teeth with well-developed marginal denticles
  6. Terminal caudal centra platycoelous

References

  1. Young, C. C. (1939). On a New Sauropoda, with Notes on Other Fragmentary Reptiles from Szechuan. Bulletin of the Geological Society of China 19(3): 279-315. Wiley. doi:10.1111/j.1755-6724.1939.mp19003005.x young1939a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the hip height estimate.

    jones2026b
  3. He, X.; Li, K.; Cai, K.; Gao, Y. (1984). Omeisaurus tianfuensis: a new species of Omeisaurus from Dashanpu, Zigong, Sichuan. Journal of Chengdu College of Geology 1984(Supplement 2): 13-32.

    Erects Omeisaurus tianfuensis on holotype ZDM T5701 from the Lower Shaximiao Formation of Dashanpu, Zigong.

    he1984b
  4. Jiang, S.; Li, F.; Peng, G. Z.; Ye, Y. (2011). A new species of Omeisaurus from the Middle Jurassic of Zigong, Sichuan. Vertebrata PalAsiatica 49(2): 185-194.

    Erects Omeisaurus jiaoi on holotype ZDM 5050 from the Lower Shaximiao Formation of Dashanpu, Zigong.

    jiang2011a
  5. Tan, C.; Xiao, M.; Dai, H.; Hu, X. F.; Li, N.; Ma, Q. Y.; Wei, Z. Y.; Yu, H. D.; Xiong, C.; Peng, G. Z.; Jiang, S.; Ren, X. X.; You, H. L. (2021). A new species of Omeisaurus (Dinosauria: Sauropoda) from the Middle Jurassic of Yunyang, Chongqing, China. Historical Biology 33(9): 1817-1829. Informa UK Limited. doi:10.1080/08912963.2020.1743286

    Erects Omeisaurus puxiani on holotype CLGPR V00005 from the lower Shaximiao Formation of Yunyang, Chongqing.

    tan2021a
  6. Dong, Z.; Zhou, S.; Zhang, H. (1983). [Dinosaurs from the Jurassic of Sichuan]. Palaeontologica Sinica, New Series C, Whole Number 162(23): 1-136. dong1983a
  7. Tang, F.; Jin, X.; Kang, X.; Zhang, G. (2001). Omeisaurus maoianus: a complete Sauropoda from Jingyan, Sichuan. Omeisaurus maoianus: a complete Sauropoda from Jingyan, Sichuan. China Ocean Press, Beijing.

    Monograph naming Omeisaurus maoianus on a skull and partial skeleton from the lower Upper Shaximiao at Jingyan, Sichuan.

    tang2001c