[2] During the late 1980s, a field crew from the Universidad Nacional Tucumán, led by Jaime Powell, uncovered forty kilometres south of Roca City, in Río Negro province, southern Argentina, the remains of a theropod near the Salitral Ojo de Agua.

It consists of the distal (lower or outermost) half of the right femur (thighbone), and a complete right tibia (inner shinbone), collected from the Allen Formation of the Malargüe Group in the Neuquén Basin.

Although Coria (2001) considered a hooked cnemial crest to be unique to Quilmesaurus,[3] Valieri et al. (2007) noted that this structure was also possessed by Aucasaurus and Majungasaurus, as well as the ambiguous abelisaurid Genusaurus.

[3] The presence of a notch in the distal articular surface of the tibia was cited by him as evidence of a possible relationship with basal Tetanurae, which would be surprising as Quilmesaurus lived during a time when South American theropod assemblages were dominated by abelisaurids and carcharodontosaurs.

[6] However, in a 2004 abstract (and later a 2007 full paper), Rubén Juárez Valieri et al. concluded that Quilmesaurus, in view of the hatchet-shaped cnemial crest, was a member of the Abelisauridae.

[7][2] Unlike members of Megalosauroidea, the tibia of Quilmesaurus does not possess a noticeable anteromedial buttress, and instead it includes a large cnemial crest.

Finally, the shallow and wide (rather than deep and thin) extensor groove excludes Quilmesaurus from Carnosauria, as does the possession of parallel upper and lower edges of the cnemial crest.

The hook-like shape of the cnemial crest suggests that Quilmesaurus was a member of the subfamily Carnotaurinae, which Sereno (1998) defined to include all abelisaurids closer to Carnotaurus than to Abelisaurus.

Although Valieri et al. (2007) considered the subfamily to include taxa such as Majungasaurus, Carnotaurus, Aucasaurus, and Rajasaurus, other studies have found different results.

Filippi et al. (2016) created a new clade, Furileusauria, to include abelisaurids more closely related to Carnotaurus than to Ilokelesia, Skorpiovenator, or Majungasaurus.

[1] Valieri et al. (2007) were unable to establish a single autapomorphy (distinctive or unique trait) of the taxon, concluding that Quilmesaurus were a nomen vanum.

[2] The Allen Formation is believed to have been a humid coastal environment which gradually transitioned from a freshwater floodplain to marshy estuaries and then shallow lagoons as sea levels rose.

[9] Plant life includes palm trees and conifers of the family Podocarpeaceae ("plum pines"), which formed dense forests and wetlands.

[12] Dinosaur remains recovered from the Allen Formation include a diverse and abundant assortment of titanosaurs (Saltasaurus, Aeolosaurus, Laplatasaurus, Rocasaurus, etc.)