Minotaurasaurus (meaning "Minos'-bull reptile") is a monospecific genus of ankylosaurid dinosaur that lived in Mongolia during the Late Cretaceous (late Campanian stage, ~75-71 Ma) in what is now the Djadochta Formation. The type and only species, Minotaurasaurus ramachandrani, is known from two skulls, a cervical vertebra and a cervical half ring. It was named and described in 2009 by Clifford Miles and Clark Miles. The holotype of Minotaurasaurus has been suspected to be illegally exported out of Mongolia. It has been suggested to be a synonym of Tarchia but more recent publications consider it as a distinct genus.

Minotaurasaurus was a medium-sized ankylosaurid, with an estimated length of 4.2 metres (13.8 feet), although it may have reached larger sizes as the type specimen represents an immature individual. Although not a lot of postcranial material is known, it would have had a tail club that may have been used for protection against predators or interspecific combat and would have been covered in protective osteoderms. It would have also had a barrel-like body, and short, robust limbs based on close relatives.

In 2003, a skull of an ankylosaurid was purchased for US$10,000 by the private fossil collector and neuroscientist Vilayanur S. Ramachandran while accompanied by Clifford Miles at the Tucson Gem, Mineral and Fossil Showcase, Arizona. The skull was put on display by Robert Gaston for the fossil dealer Hollis Butts, who Ramachandran purchased it from.

The stratigraphic position was stated as being from the Gobi Desert of either Mongolia or China due to the provenance being unknown at the time. In 2006, Clifford Miles and his brother Clark Miles attempted to publish the description of the skull in a Polish Journal but was promptly rejected as the specimen was seemingly obtained illegally from Mongolia. Two years later, the authors stated that the specimen had come from the Barun Goyot Formation but later stated that they could not confirm its origin. The skull would later be described and named in 2009. The publication was later criticised by palaeontologists such as Mark Norell, Phillip J. Currie and Bolortsetseg Minjin due to the questionable origins of the specimen.

The holotype specimen, INBR21004, consists of a skull with lower jaws and predentary. The type specimen is currently housed at the Victor Valley Museum in Apple Valley, California. The generic name, Minotaurasaurus, is derived from the Minotaur and the Greek word "sauros" (lizard), in reference to the bull-like appearance of the holotype skull. The specific name, ramachandrani, honours V. S. Ramachandran, who purchased the type specimen.

In 2013, a Society of Vertebrate Paleontology abstract book mentioned the discovery of a second specimen of Minotaurasaurus (MAE 98 179) from the Uhkaa Tolgod locality of the late Campanian Djadochta Formation in the Nemegt Basin. The specimen consists of a skull, axis and first cervical half-ring, and it is part of the collection of the Mongolian Academy of Sciences. MAE 98 179 was reported as having insect burrows that continues into a pattern which is only seen in Late Cretaceous Gobi deposits. Penkalski & Tumanova (2016) would later describe the specimen, which was used to establish the stratigraphic position of the type specimen and the validity of the taxon, as before it was suggested by Arbour et al. (2014) and Arbour & Currie (2015) to be from the Barun Goyot Formation and a junior synonym of Tarchia kielanae. Its validity was also tested by Arbour & Currie (2012) by using a retrodeformation and finite element analysis, which found that many of its diagnostic features were likely not caused by deformation.

Miles & Miles (2009) gave Minotaurasaurus an estimated length of at least 4.2 metres (13.8 feet), although it may have attained larger sizes as the type specimen, and only known specimen at the time, represents an immature individual based on the unfused osteoderms.

Penkalski & Tumanova (2016) established numerous distinguishing traits of Minotaurasaurus. The paroccipital processes are not present laterally to the squamosal horns due to presence of a small and dorsoventrally shallow occiput. The skull roof possessing an unfused occiput. Basioccipital foramen that are either small or absent. Highly sculptured squamosal horns that are dorsoventrally narrow and cylindrical in shape. Non prominent nuchal caputegulae that angle caudolaterally. The presence of two distinct supraorbital apices. Frontal caputegulae that aren't arranged at right angles but with nasofrontal caputegulae that are elongated transversely and are ridge-like. The presence of a deep notch in the lacrimal. The presence of two pairs of internarial osteoderms, unlike the presence of a single osteoderm as in Tarchia and Saichania. An overall small skull that is broad. A more horizontal pterygoid body. A mandibular osteoderm that extends towards the front end of the tooth row. Other distinguishing traits include the occiput being more visible in dorsal view, an occipital condyle that is protrudes less towards the underside in caudal view and a skull that is proportionally lower and wider than that of Tarchia.