Genus: Loncosaurus AMEGHINO, 1899
Etymology: As per Ben Cresiler “from Araucanian lonco “head”, commonly used in Chilean and Argentine geographical names; the allusion in this case is obscure and Greek, sauros, “lizard”: “lonco lizard”?
= Loncasaurus AMEGHINO, 1898 (sic)
= Longosaurus ROTH, 1900 (sic)

Species: argentinus AMEGHINO, 1899
Etymology: In reference to Argentina, the country of origin.
= Megalosaurus argentinus (AMEGHINO, 1898) (nomen dubium)
= Longosaurus argentinus ROTH, 1900 (sic)

Holotype: MACN 11629

Locality: Par Aik, rio Schuen, territory of Santa Cruz, Argentina.

Horizon: Cardiel Formation (= “Guarantic” Formation).

Biostratigraphy:

Age: Santonian or Lower Campanian Stage, Senonian Stage, Gulf Epoch, Late Cretaceous.

Note: Or probably Coniacian Stage.

Material: Proximal end of femur.