Open Paleo

Guaibasaurus

Bonaparte et al., 1999 GWIE-bah-SAWR-us

Named after the Guaíba River region of Rio Grande do Sul, Brazil, where it was discovered, combined with Greek sauros (lizard); meaning 'Guaíba lizard'

227.3–205.7 million years ago Norian, Late Triassic
Late Triassic stages

Guaibasaurus is an extinct genus of basal saurischian dinosaur known from the Late Triassic Caturrita Formation of Rio Grande do Sul, southern Brazil. Most analyses recover it as a sauropodomorph, although there are some suggestions that it was a theropod instead. In 2016 Gregory S. Paul estimated it at around 2 meters long (6.6 ft) and 10 kg (22 lbs), whereas in 2020 Molina-Pérez and Larramendi listed it at 3 meters (10 ft) and 35 kg (77 lbs).

Under dispute

Guaibasaurus candelariensis has an unstable position: originally a basal theropod, it is recovered as a basal sauropodomorph by recent analyses (Novas and colleagues, 2010, within Guaibasauridae; Hechenleitner and colleagues, 2025, as sister to Bagualosauria). The family Guaibasauridae is not adopted, being contested and effectively monotypic.

Diagnosis

  1. Midanterior dorsal neural arches with large pneumatic cavities opening below the base of the transverse process
  2. Undivided infradiapophyseal lamina combined with a well-developed parapophyseal-prezygapophyseal lamina and a deep fossa below it
  3. Acetabulum nearly closed, with only incipient reduction of the medial wall, plus an extremely large crista supracetabularis and a well-developed fossa brevis
  4. Sacral centra of strongly unequal size, the anterior centrum about twice the volume of the next
  5. Femur with a small anterior trochanter, a dorsolateral ridge above the anterior trochanter, and no trochanteric shelf
  6. Calcaneum transversely narrow with a pronounced ventromedial process; metatarsal V strongly reduced and without phalanges while metatarsal I is unreduced

Species

Guaibasaurus candelariensis Bonaparte et al., 1999

Type species

Named for Candelária, a city in Rio Grande do Sul, Brazil, near the fossil locality where the holotype was found.

Holotype
MCN-PV 2355 , Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul
Material
A partial postcranial skeleton: dorsal and sacral vertebrae, ten articulated caudals with chevrons, dorsal ribs, scapulocoracoids, both ilia, pubes, ischia, and most of both hind limbs and feet.
Horizon
Caturrita Formation, Norian, Late Triassic , 227.3–205.7 million years ago
Locality
Sesmaria do Pinhal 2, Rio Grande do Sul, Brazil Bonaparte and colleagues (1999) place the holotype 100 m south of highway RS-287, some 7.5 km west of Candelária, without naming the site; Novas and colleagues (2021) call it Sesmaria do Pinhal 2.

References

  1. Bonaparte, J. F.; Ferigolo, J.; Ribeiro, A. M. (1999). A new early Late Triassic saurischian dinosaur from Rio Grande do Sol state, Brazil. Proceedings of the Second Gondwanan Dinosaur Symposium, National Science Museum Monographs 15: 89-109. bonaparte1999b
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the hip height estimate.

    jones2026b
  3. Hechenleitner, E. M.; Martinelli, A. G.; Rocher, S.; Fiorelli, L. E.; Juarez, M.; Taborda, J. R. A.; Desojo, J. B. (2025). A long-necked early dinosaur from a newly discovered Upper Triassic basin in the Andes. Nature 648(8094): 634-639. Springer Science and Business Media LLC. doi:10.1038/s41586-025-09634-3

    Described new long-necked early dinosaur, recovering Guaibasaurus as basal sauropodomorph.

    hechenleitner2025a
  4. Novas, F. E.; Ezcurra, M. D.; Chatterjee, S.; Kutty, T. S. (2010). New dinosaur species from the Upper Triassic Upper Maleri and Lower Dharmaram formations of Central India. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101(3-4): 333-349. Cambridge University Press (CUP). doi:10.1017/S1755691011020093

    Recovered Guaibasaurus as basal sauropodomorph within Guaibasauridae.

    novas2010a
  5. Novas, F. E.; Agnolín, F. L.; Ezcurra, M. D.; Müller, R. T.; Martinelli, A. G.; Langer, M. C. (2021). Review of the fossil record of early dinosaurs from South America, and its phylogenetic implications. Journal of South American Earth Sciences 110: 103341. doi:10.1016/j.jsames.2021.103341

    Names the holotype site Sesmaria do Pinhal 2.

    novas2021a