Mauriciosaurus (meaning "Mauricio [Fernández Garza's] reptile") is a genus of polycotylid plesiosaur from the Late Cretaceous of Mexico. It contains a single species, M. fernandezi (also named after Fernández Garza), described in 2017 by Eberhard Frey and colleagues from a single well-preserved juvenile specimen about 2 metres (6 ft 7 in) long. Morphologically, it is overall most similar to the polycotyline polycotylids Trinacromerum and Dolichorhynchops. However, several features separate Mauriciosaurus from all other polycotylids, warranting the naming of a new genus. These include the sophisticated pattern of ridges on the bottom of the parasphenoid bone on its palate; the narrow openings in the palate bordered by the pterygoid bones; the lack of perforations in the surface of the coracoid; and the highly unusual arrangement of gastralia, or belly ribs, which is only otherwise seen in the non-polycotylid Cryptoclidus. Partially as a consequence of the oxygen-poor environment that the specimen was preserved in, the type specimen Mauriciosaurus is notable for possessing well-preserved soft-tissues. 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. Additionally, a heavily-pigmented lining protected the organs of the body cavity from UV exposure. After death, the sediment allowed the contour fat to preserve into adipocere instead of putrefying, which preserved most of the epidermal soft tissue save for that of the belly. 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. Inoceramid bivalves represent the only endemic benthic fauna at the site; other fossil organisms known from Vallecillo include invertebrates such as ammonites and barnacles that grew on those ammonites, as well as vertebrates consisting of various fish, aigialosaurid mosasaurs, and turtles. 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.
Discovery and naming
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. The specimen has been broken into 28 slabs, which collectively preserve a nearly-complete and articulated skeleton, missing only the left coracoid, parts of the flippers, and the tip of the tail (which were lost during collection by the workers).
INAH CPC RFG 2544 P.F.1 was found in a 7.7 metres (25 ft) section of laminated limestone mixed with marl, part of the plattenkalk Konservat-Lagerstätte (fine limestone deposits that exquisitely preserve animals) within the Cenomanian-Turonian Agua Nueva Formation. The plattenkalk is quite widespread, being largely concentrated around Vallecillo but spanning an area of 10,000 square kilometres (3,900 sq mi). Outside of these deposits, macroscopic fossils are relatively rare in the Agua Nueva. Detailed biostratigraphic zonation has been conducted for the Vallecillo plattenkalk; the presence of the vascoceratid ammonite Mammites nodosoides allows the slab containing Mauriciosaurus to be dated to the early Turonian portion of the plattenkalk. 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). The genus and species name, Mauriciosaurus fernandezi, is in honour of Mauricio Fernández Garza, who has provided the specimen for scientific study, in addition to providing funding for both research at Vallecillo and public science education in Nuevo León.
Description
Mauriciosaurus is a short-necked plesiosaur, bearing a drop-shaped body with a small tail. The type specimen of Mauriciosaurus would have measured 1.9–2.1 metres (6 ft 3 in – 6 ft 11 in) long in total, 1.5 metres (4 ft 11 in) wide at the flippers and weighed 79 kilograms (174 lb). However, this specimen is immature, judging by the lack of fusion in the cervical vertebrae; 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; the short ischia; and the presence of gaps (filled by extensive cartilage in life) between the long bones of the flippers. The palate is mineralized, suggesting that the specimen was still at least a subadult. Adult individuals would have grown up to twice the length of the type specimen.
Skull
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