Monquirasaurus ("Monquirá lizard") is an extinct genus of giant short-necked pliosaurs who lived during the Early Cretaceous (Aptian) in what is now Colombia.

One species is known, M. boyacensis, described in 2021 from an almost complete fossil skeleton, discovered in 1977 in the town of Villa de Leyva, located in Boyacá.

This identification was due to the fact that the holotype specimen was banned from local access, and the descriptions were published with the help of photos.

The site where Monquirasaurus was discovered is the Paja Formation, that was once an environment containing a vast diversity of marine reptiles, including other large related pliosaurs, such as Stenorhynchosaurus and Sachicasaurus.

[4][5] In 2021, Noè & Gómez-Pérez suggested that a sexually mature, sub-adult individual would have measured 8 metres (26 ft) long.

The cranium does not only suffer from crushing, but most of the dorsal surface is also heavily weathered and many bones are missing, making it almost impossible to observe most of the skull sutures.

[1] The mandible is robust and resembles classic pliosaurid morphology with large caniniform teeth housed at the anterior margin of the bone.

The anterior dentition is markedly anisiodont and interlocking, while more posterior areas of the skull have tooth rows overlapping.

The anterior expansion of the premaxilla contains 4 teeth on each side, with premaxillary tooth 2 being the largest, extending halfway down the mandible.

Between the last preserved premaxillary and first maxillary caniniform extends a toothless gap or diastema, equivalent in diameter to the area taken up by a large tooth.

[1] The body of Monquirasaurus was 4.65 metres (15.3 ft) long along the vertebral column, not including the skull and missing tail.

The appendicular skeleton is only partly preserved, with all limbs missing the distal end of the flippers and girdles obscure by the overlaying torso.

The authors instead suggest that it, alongside Sachicasaurus and Acostosaurus, may have been part of an unrecognized lower Cretaceous non-Brauchaucheniin family of pliosaurs.