[3] A partial skull and several postcranial elements such as vertebrae and dermal plates from the Bajo de la Carpa Formation[4] in Argentina and another partial skull and several unprepared postcranial elements from the Anacleto Formation, Argentina, were assigned to Peirosaurus by Gasparini, Chiappe and Fernandez (1991) and Praderio, Martinelli and Candeiro (2008), respectively.

Sertich, Alberto C. Garrido and Ángel M. Praderio concluded that the traits which used to unite the holotype (from Brazil) and the referred material from Argentina are shared with other peirosaurids and some other mesoeucrocodylians.

They reassigned the Argentinian specimens to a new genus, Gasparinisuchus, and although overlapping materials between the genera are limited to the premaxilla and the dentition, Gasparinisuchus can be differentiated from Peirosaurus on the basis of its broad, rounded rostrum, anteroposteriorly short premaxilla, reduced perinareal fossa, and short premaxillary interdental spaces.

Peirosaurus shares a number of features with the closely related genus Uberabasuchus, found from a nearby locality in Uberaba.

[5] Though many of the features of the premaxilla and dentition of Peirosaurus are widespread among peirosaurids and many mesoeucrocodylians, several are shared exclusively with Uberabasuchus.