In life, each of its four flippers bore a flexible trailing edge such that they formed hydrofoils, and contour fat created a drop-like outline of the body by merging the torso and immobile tail into a single unit.

Both of these soft-tissue traits would have improved the animal's hydrodynamic performance, making it a fast swimmer comparable to modern leatherback sea turtles.

The oxygen-poor deposits that Mauriciosaurus was preserved in, collectively known as the Vallecillo plattenkalk, would have represented the bottom of a continental shelf about 500 kilometres (310 mi) offshore in the prehistoric Gulf of Mexico.

The type specimen of Mauriciosaurus is associated with an ammonite, Mammites nodosoides, which is present only in the Turonian interval of the Vallecillo deposits, allowing it to be dated to that age.

The type and only known specimen of Mauriciosaurus was found in the summer of 2011 by workers at a laminated limestone quarry near the town of Vallecillo, in the state of Nuevo León, Mexico.

It is labelled under the collection number INAH CPC RFG 2544 P.F.1 (INAH standing for the Instituto Nacional de Antropología e Historia, or National Institute of Anthropology and History) at the Museo del Desierto in Saltillo, Coahuila, Mexico; currently, however, it is on display currently at the Museo Papalote Verde in Monterrey, the capital of Nuevo León.

[1] Eberhard Frey, Eric Mulder, Wolfgang Stinnesbeck, Héctor Rivera Sylva, José Padilla Gutiérrez, and Arturo González González described the specimen in 2017, formally naming it as a new taxon in a paper submitted to the Boletín de la Sociedad Geológica Mexicana (Bulletin of the Geological Society of Mexico).

[1] However, this specimen is immature, judging by the lack of fusion in the cervical vertebrae;[6] the coracoids bearing no forward projections that interlock with the clavicles; the thin bones of the shoulder and hip girdles; the lack of a ridge on the top surface of the scapula;[7] the short ischia;[8] and the presence of gaps (filled by extensive cartilage in life) between the long bones of the flippers.

All of the teeth are of the same shape, being four times taller than they are wide with conical and recurved tips; the smallest tooth, from the back of the mouth, is about a quarter the size of the largest.

However, they are unusually narrow and oval-shaped in Mauriciosaurus, whereas they are wider and more rounded in Trinacromerum due to the concave inner margins of the pterygoid and parasphenoid.

[1] In addition to the aforementioned forward projections, the trapezoidal coracoid of Mauriciosaurus differs from those of Dolichorhynchops and Trinacromerum in that it lacks perforations along its midline and at its back margin.

[1] One of the traits that allies Mauriciosaurus with other polycotyline polycotylids is its slightly S-shaped humerus, which is approximately 1.6 times as long as it is wide.

The first type consists of a largely amorphous glossy black material, bearing some traces of fibres, or wrinkles, which is preserved only within the body cavity, mostly on the right side of the torso.

At the junction between the femur and the body, they become larger, more trapezoidal, and radially arranged to form a folding surface; meanwhile, on the back edge of the flippers, these structures become sub-circular, which enhances the flexibility of the skin.

This substance, which is crisscrossed by a series of straight furrows that divide it into rectangular or trapezoidal segments, is of unknown, but probably epidermal, provenance.

Finally, a grey, glossy, amorphous substance, which forms a thick cone surrounding the base of the tail, probably represents subcutaneous fat.

[1] 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.

[20][8] It differs from both genera in the W-shaped ridges present on the back of the bottom surface of its pterygoid,[14][16][17][18] as well as the possession of more tooth positions in the premaxilla and maxilla.

[13][14][15] 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 living squamates which reside in deserts or at high altitudes, pigmentation of the peritoneum protects the body cavity against solar ultraviolet radiation, thereby preventing damage to reproductive organs.

[25] As a surface-swimming plesiosaur, Mauriciosaurus would have been frequently exposed to solar radiation, and thus a pigmented peritoneum would have been advantageous particularly during the early stages of its life.

[1] Frey et al. hypothesized the thick contour fat of plesiosaurs such as Mauriciosaurus may account for the scarcity of preserved skin from members of the group.

[1] During the Turonian, the Vallecillo plattenkalk would have been part of a relatively flat (i.e. low relief) open-ocean deep shelf,[38][39] located about 500 kilometres (310 mi) offshore at the junction between the Western Interior Seaway and the prehistoric Gulf of Mexico.

The oxygen-poor seafloor would have prevented carnivores, scavengers, or substrate-dwelling animals from feeding on the deposited carcasses, explaining the quality of preservation along with the absence of waves or currents.

By far the most abundant benthic invertebrates are inoceramid bivalves, which may have lived in symbiosis with chemoautotrophic microbes in order to survive in the low-oxygen conditions.

Taxa that may have lived alongside Mauriciosaurus, from the Mammites nodosoides - Mytiloides kossmati biozone, include the holostean Paranursallia gutturosum,[46][47] the pachyrhizodontid Goulmimichthys roberti,[48] the plethodid Tselfatia formosa,[46] and the alepisauriform Rhynchodercetis sp.

[44][45][51] Tetrapods are much rarer in the Vallecillo plattenkalk, consisting of the well-preserved back half of the aigialosaurid mosasaur Vallecillosaurus bearing soft-tissue impressions, three turtles representing two taxa, and a tooth referred to the pliosaur "Polyptychodon".