Open Paleo

Isanosaurus

Buffetaut et al., 2000 ee-sahn-o-SAWR-us

Named for Isan, the northeastern region of Thailand, combined with Greek 'sauros' meaning 'lizard'. The species name honors P. Attavipach, a supporter of paleontological research in Thailand.

227.3–143.1 million years ago Norian–Tithonian, Late Triassic–Late Jurassic

Isanosaurus is an extinct genus of sauropod dinosaur from Thailand. It was originally dated to approximately 219-199 million years ago during the Late Triassic (late Norian to Rhaetian stages), which would make it one of the oldest known sauropods. Its age was later considered uncertain, and may be Early Jurassic or even as young as Late Jurassic. The only species is Isanosaurus attavipachi. Though important for the understanding of sauropod origin and early evolution, Isanosaurus is poorly known. Exact relationships to other early sauropods remain unresolved.

Under dispute

Isanosaurus is placed as a basal, non-eusauropodan sauropod, but its position at the sauropod/sauropodiform boundary is unsettled. Pol and Gomez (2022) recover it within Sauropoda but outside Eusauropoda (grouped with Gongxianosaurus and vulcanodontids), whereas Rauhut and colleagues (2020) recover it as a non-sauropodan sauropodiform lying immediately outside Sauropoda under the node-based definition (Vulcanodon plus Saltasaurus).

Diagnosis

  1. Robust femur with very prominent, acuminate, S-shaped fourth trochanter located in proximal half
  2. Opisthocoelous cervical vertebrae with parapophyses at mid-height
  3. Strong ventral median ridge on cervical centra
  4. Dorsal neural arch remarkably tall with spine longer rostrocaudally than transversely
  5. Scapula with moderate dorsally rounded proximal expansion and slight distal expansion

Species

Isanosaurus attavipachi Buffetaut et al., 2000

Type species

Named for P. Attavipach, a supporter of paleontological research in Thailand and former Director General of the Thai Department of Mineral Resources.

Holotype
CH4-1 , Department of Mineral Resources
Material
Associated skeletal elements: one cervical, one dorsal and six caudal vertebral centra, neural arch of posterior dorsal vertebra, two chevron bones, fragmentary ribs, right sternal plate, right scapula, left femur.
Horizon
Nam Phong Formation, Norian–Tithonian, Late Triassic–Late Jurassic , 227.3–143.1 million years ago
Locality
Phu Nok Khian hill, Chaiyaphum, Thailand No paper places the Phu Nok Khian site in either part of the Nam Phong. Buffetaut and colleagues (2000) give "dark red sandstones of the Nam Phong Formation", which outcrop palynology dates late Norian to Rhaetian. Hanta and colleagues (2023) call the type locality's beds "likely the Upper Nam Phong Formation" from their lithology, the Upper Nam Phong being no older than Pliensbachian and probably Late Jurassic. Rauhut and colleagues (2020) state that "the Upper Nam Phong Formation that has yielded Isanosaurus has recently been dated as Early Jurassic", citing Racey and Goodall (2009), who do not mention the genus. Racey and Goodall (2009) caution that the boundary "would be difficult to detect at outcrop", so its horizon may belong to either part.

References

  1. Buffetaut, E.; Suteethorn, V.; Cuny, G.; Tong, H.; Le Loeuff, J.; Khansubha, S.; Jongautchariyakul, S. (2000). The earliest known sauropod dinosaur. Nature 407(6800): 72-74. Springer Science and Business Media LLC. doi:10.1038/35024060 buffetaut2000a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the mass and hip height estimates.

    jones2026b
  3. Rauhut, O. W. M.; Holwerda, F. M.; Furrer, H. (2020). A derived sauropodiform dinosaur and other sauropodomorph material from the Late Triassic of Canton Schaffhausen, Switzerland. Swiss Journal of Geosciences 113(1). Pensoft Publishers. doi:10.1186/s00015-020-00360-8

    Recovered Isanosaurus as a non-sauropodan sauropodiform just outside Sauropoda, and takes its Upper Nam Phong horizon as Early Jurassic after Racey and Goodall (2009).

    rauhut2020a
  4. Pol, D.; Gomez, K.; Holwerda, F. M.; Rauhut, O. W. M.; Carballido, J. L. (2022). Sauropods from the Early Jurassic of South America and the Radiation of Eusauropoda. South American Sauropodomorph Dinosaurs: Record, Diversity and Evolution 131-163. Springer International Publishing. doi:10.1007/978-3-030-95959-3_4

    Recovered Isanosaurus outside Eusauropoda, grouped with Gongxianosaurus and vulcanodontids.

    pol2022a
  5. Racey, A.; Goodall, J. G. S. (2009). Palynology and stratigraphy of the Mesozoic Khorat Group red bed sequences from Thailand. Geological Society, London, Special Publications 315: 69-83. doi:10.1144/SP315.6

    Splits the Nam Phong into a Late Triassic lower part and an Upper part no older than Pliensbachian, by seismic and well data.

    racey2009b
  6. Hanta, R.; Sekiya, T.; Shibata, M.; Naksri, W.; Tucker, R. T. (2023). Hatchling and early juvenile of early sauropod from the early Middle Jurassic Nam Phong Formation, Chaiyaphum Province, northeastern Thailand. Paleontological Research 28(3): 222-239. doi:10.2517/pr230002

    Assigns the type locality's beds to the Upper Nam Phong Formation on their lithology.

    hanta2023a