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. However, some features do support its placement within Ceratosauria. These include a pronounced cnemial crest of the tibia and large mesiodistal crest of the femur. The asymmetrical distal part of the tibia and small socket for the astragalus specifically place it within the family Abelisauridae. The preserved bones share features with various abelisaurid taxa throughout the family, although such similarities are widespread and seemingly pop up at random among the taxa, thus making more specific placement difficult. 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.However, the validity of Carnotaurinae has been debated. Although Valieri et al. (2007) considered the subfamily to include taxa such as Majungasaurus, Carnotaurus, Aucasaurus, and Rajasaurus, other studies have found different results. Tortosa et al. (2014) found that Carnotaurinae was an invalid group, as very few abelisaurids could actually apply to the definition set forth by Sereno. According to their analysis, Aucasaurus and Carnotaurus were actually closer to Abelisaurus than they were to Majungasaurus and Rajasaurus, thus forcing the latter two taxa to be excluded from the subfamily. Quilmesaurus was retained as close to Aucasaurus and Carnotaurus, although Sereno's name and definition of Carnotaurinae was completely demolished. In its place the tribe Carnotaurini was used, which includes all abelisaurids descended from the last common ancestor of Aucasaurus and Carnotaurus. Tortosa et al. (2014)'s result has largely been supported over that of Valieri et al. (2007). Filippi et al. (2016) created a new clade, Furileusauria, to include abelisaurids more closely related to Carnotaurus than to Ilokelesia, Skorpiovenator, or Majungasaurus. They included Quilmesaurus among the furileusaurians. 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. Paleoecology 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. A diverse assemblage of aquatic life inhabited the area, including various fish, frogs, and turtles. More recent intervals of the formation even include a few marine reptiles, such as various plesiosaurs including elasmosaurids and polycotylids.