Tarchia was a large, herbivorous dinosaur that roamed modern-day Mongolia during the Late Cretaceous period, approximately 70 to 72 million years ago. As a member of the ankylosaurid family, it is often likened to a “living tank” due to its extensive body armor. The name Tarchia comes from the Mongolian word “tarkhi,” meaning “brain,” a reference to its larger braincase compared to its relatives. Fossils were first discovered by a Polish-Mongolian expedition in the Gobi Desert in 1970.
Physical Anatomy
Tarchia possessed a broad, low-slung body, a characteristic feature of ankylosaurids. Estimates place its size at around 5.5 to 6 meters (18 to 20 feet) in length, with a weight of up to 2.5 to 3 metric tons. Its powerful, short legs were positioned directly under its wide body, providing the strength to carry its substantial mass and armor.
The skull of Tarchia was wide and heavily ossified, meaning many of the skull bones were fused together for strength. The skull also featured ornamentation, including rows of bumps and spikes on its cheeks. Its beak was wider than that of its close relatives, an adaptation suited for its specific feeding habits.
Defensive Armor and Tail Club
The most prominent feature of Tarchia was its defensive armor. Its back and head were covered in osteoderms—bony plates embedded directly into the skin. These plates formed a shield over the animal’s most vulnerable areas, protecting it from large predators.
Its primary weapon was its tail club. The last several vertebrae of the tail were fused and stiffened to form a handle-like structure that terminated in a large, heavy mass of bone. This created a powerful mace that could be swung with considerable force.
The tail club was likely used to fend off predators like Tarbosaurus, a close relative of Tyrannosaurus. Evidence of Tarbosaurus tooth marks on a Tarchia skull confirms it was a target for these carnivores. The club could deliver debilitating blows to an attacker’s legs or ribs, and some evidence suggests they were also used in fights between two Tarchia.
Habitat and Diet
Fossils of Tarchia are found in Mongolia’s Barun Goyot and Nemegt Formations, representing its Late Cretaceous habitat. This environment was not a barren desert but a varied landscape of river channels, floodplains, and oases. The region was a sandy expanse with dunes and pockets of vegetation that supported large herbivores.
As a herbivore, Tarchia was a low-level browser with a wide, beak-like mouth adapted for cropping ground-level plants. The shape of its mouth suggests it was a selective feeder, choosing specific types of vegetation. Its diet likely consisted of tough, dry plants such as ferns and cycads that grew in its semi-arid environment. Tarchia would have required a large digestive system to process this fibrous plant matter.