Macrocephalosaurus is a genus of rhynchosaurs (beaked, archosaur-like reptiles) from the Late Triassic period (Carnian stage) of southern Brazil.

[1] The type species of Macrocephalosaurus, M. mariensis, was described in 1933 by Jaci Antonio Louzada Tupi Caldas on the basis of MCN 1867, a complete specimen from the upper member of the Santa Maria Formation in Rio Grande Do Sul State, southern Brazil.

[2][3] Nevertheless, Langer and Schultz (2000) listed M. mariensis as a valid species within Hyperodapedon, as H.

[5] In their cladistic analysis of the newly described taxon Beesiiwo, Fitch et al. (2023) recovered Macrocephalosaurus as more closely related to Supradapedon and Teyumbaita rather than Hyperodapedon gordoni (the type species of Hyperodapedon) or Oryctorhynchus.

The following cladogram is based on the phylogenetic analysis by Fitch et al. (2023):[1] Isalorhynchus genovefae Beesiiwo cooowuse Oryctorhynchus bairdi Hyperodapedon gordoni "Zimbabwe Form" Paradapedon huxleyi "Scaphonyx" sanjuanensis Macrocephalosaurus mariensis "Hyperodapedon" tikiensis Supradapedon stockleyi "Hyperodapedon" huenei Teyumbaita sulcognathus