In 2017, Mauriciosaurus was assigned to the Polycotylidae by Frey et al.
based on characteristics of the pterygoid, mandible, humerus, and phalanges as previously described.
Additional characteristics used to refer Mauriciosaurus to Polycotylidae included the reduced number of cervical vertebrae relative to other plesiosaurs in the Leptocleidia, as well as the presence of several additional ossifications supporting the epipodials of the flippers.
Within the Polycotylidae, Mauriciosaurus was assigned to the clade Polycotylinae based on the length/width ratio of the humerus, the lack of an opening (the antebrachial foramen) between the radius and ulna, the presence of three distal tarsals, the primary epipodials being wider than they are long, and the presence of more than 20 vertebrae in the trunk.

Within the Polycotylinae, Frey et al.
considered Mauriciosaurus to be morphologically closest to Dolichorhynchops and Trinacromerum.
Mauriciosaurus is more similar to Dolichorhynchops in the rounded ends of its humerus and femur; meanwhile, it is more similar to Trinacromerum in its expanded pterygoid rods, bifurcated front end of the parasphenoid, and relatively longer phalanges.
It differs from both genera in the W-shaped ridges present on the back of the bottom surface of its pterygoid, as well as the possession of more tooth positions in the premaxilla and maxilla.
In addition to these characteristics, others used by Frey et al.
to diagnose Mauriciosaurus as a new genus included the narrow interpterygoid vacuities, the lack of perforations in the coracoids, and the highly specialized arrangement of the gastralia.
In 2017, Mauriciosaurus was assigned to the Polycotylidae by Frey et al. based on characteristics of the pterygoid, mandible, humerus, and phalanges as previously described. Additional characteristics used to refer Mauriciosaurus to Polycotylidae included the reduced number of cervical vertebrae relative to other plesiosaurs in the Leptocleidia, as well as the presence of several additional ossifications supporting the epipodials of the flippers. Within the Polycotylidae, Mauriciosaurus was assigned to the clade Polycotylinae based on the length/width ratio of the humerus, the lack of an opening (the antebrachial foramen) between the radius and ulna, the presence of three distal tarsals, the primary epipodials being wider than they are long, and the presence of more than 20 vertebrae in the trunk.
Within the Polycotylinae, Frey et al. considered Mauriciosaurus to be morphologically closest to Dolichorhynchops and Trinacromerum. Mauriciosaurus is more similar to Dolichorhynchops in the rounded ends of its humerus and femur; meanwhile, it is more similar to Trinacromerum in its expanded pterygoid rods, bifurcated front end of the parasphenoid, and relatively longer phalanges. It differs from both genera in the W-shaped ridges present on the back of the bottom surface of its pterygoid, as well as the possession of more tooth positions in the premaxilla and maxilla. In addition to these characteristics, others used by Frey et al. to diagnose Mauriciosaurus as a new genus included the narrow interpterygoid vacuities, the lack of perforations in the coracoids, and the highly specialized arrangement of the gastralia.
Mauriciosaurus