Tarchia

Phylogeny: Dinosauria > Ornithischia > Genasauria > Thyreophora > Thyreophoroidea > Eurypoda > Ankylosauria > Euankylosauria > Ankylosauridae > Ankylosaurinae

Overview: Like all ankylosaurs, Tarchia was a sturdily built, heavily armored animal. Its body was slung low to the ground, supported by four short, but strong legs. Ankylosaur armor was formed by an array of bony masses, called osteoderms, growing within its skin. Modern crocodiles and alligators have similar dermal armor on their backs today, though not to the same extent. Tarchia possessed armor over its whole back, along its sides, down its tail, across its neck and even on its head. Its osteoderms took different forms depending on where they were located, including oval-shaped masses across the back, spinier ones along the sides or closely packed, tile-shaped masses over the skull. Tarchia belonged to the ankylosaur family Ankylosauridae, which made it more closely related to the famous Ankylosaurus than it was to nodosaurid ankylosaurs like Hylaeosaurus or Edmontonia. Ankylosaurids usually possessed bony clubs on the ends of their tails, affixed to rows of fused tail vertebrae. This was its more active means of defense.

Tarchia needed extensive armor, considering it had to contend with powerful predatory dinosaurs like Tarbosaurus – a close relative of North America’s Tyrannosaurus. Other herbivores in the region included titanosaurian sauropods like Nemegtosaurus and a wide array of ceratopsians and ornithopods. The first known specimens of Tarchia were found in by Polish and Mongolian fossil hunters in the 1970’s, in what is now the Gobi Desert of Mongolia. Described in 1977, referred fossil material included parts of its braincase, which inspired its generic name, meaning “brainy one” in Mongolian. The creature’s brain itself wasn’t very large. These fossils were found within Mongolia’s Barun Goyot Formation, but more fossils would also be attributed to Tarchia from the geologically younger Nemegt Formation. Mongolia at this time was transitioning between an arid, desert-like environment and a somewhat wetter one, which is represented by the rock deposits within the formations themselves.