Shamosaurus is an extinct genus of herbivorous basal ankylosaurid ankylosaur from Early Cretaceous (Aptian to Albian stage) deposits of Höövör, Mongolia.
In 1977, a Soviet-Mongolian expedition discovered the skeleton of an unknown ankylosaurian at the Chamrin-Us site in Dornogovi Province. This was the first discovery of an ankylosaur in the Lower Cretaceous of Mongolia.[1]
In 1983, Tatyana Tumanova named and described the type species Shamosaurus scutatus. The generic name is derived from Mandarin sha mo, "sand desert", the Chinese name for the Gobi. The specific name means "protected by a shield" in Latin, a reference to the body armour.[1]
Shamosaurus is known from the holotype PIN N 3779/2, collected from the Dzunbain Formation, equivalent to the Khukhtekskaya Formation and dating from the Aptian-Albian, about 115 million years old. It consists of a complete skull, lower jaws and partial postcranial skeleton with armor. Only the skull was described in 1983.[1] Later the specimens PIN 3779/1, a skull piece, and PIN 3101, a lower jaw, were referred. The fossils are part of the collection of the Palaeontological Institute at Moscow. The holotype skull is exhibited there, together with two cervical halfrings.[2]
Shamosaurus was a medium-sized ankylosaurian. In 2010, Gregory S. Paul estimated its body length at 5 metres (16 ft) , its weight at 2 tonnes (2.2 short tons).[3] In 2012 Holtz gave a higher estimation of 7 meters (23 ft).[4]
In 2014, Victoria Megan Arbour gave a revised list of distinguishing traits. The osteoderms on the skull roof are not very pronounced nor separated as distinctive caputegulae, head tiles. The squamosal horns on the rear skull corners are short and slightly rounded. The quadratojugal horn on the cheek has its apex in the middle. The rear rim of the skull roof has no clear (nuchal) processes.[2]