Genus: Chacaicosaurus FERNANDEZ, 1994
Etymology: Chacaio Sur, Department of Zapala, Neuquen Province, Northwestern Patagonia, Argentina, refers to the area where the holotype was found, and saurus in Greek, sauros, "lizard": Chacaico lizard.

Species: cayi (FERNANDEZ, 1994) FERNANDEZ, 2007
Etymology: Named after Cay, god of the sea of Araucanian mythology.
= Chacaicosaurus cayi FERNANDEZ, 1994

Holotype: Museo Prof. J. Olsacher, Zapala, Neuquen Province, Argentina; MOZ 5803 PV

Locality: Chacaio Sur, Department of Zapala, Neuquen Province, Northwestern Patagonia, Argentina.

Horizon: Los Molles Formation.

Biostratigraphy: Emilea giebeli zone, subzone of Emilea formis.

Age: Early Bajocian Stage, Lower Dogger Epoch, Middle Jurassic.

Material: A complete skull with an associated forelimb, proximal fragment of an humerus and femur, atlas-axis and 4 cervical vertebrae and isolated phalanges.

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