Tarchia lived during the late Cretaceous Era. They were very small for the era sharing the same time as the T-rex and other massive creatures. Evolution has it's way around they fitting into evolution with their defensive skills.
The Tarchia had a heavy armored body with a hard shell on its back. This was pretty common with all of dinosaurs in its group the Thyreophoran which is the same group that the Stegosaurus is in. Also another wild feature was that the Tarchia had a club at the end of its tail. The vertebrae on the end of the tail were fused together so the club on the end of the tail could be swung crazy in all directions stunning a carnivore enough to run away. It would something like getting hit with a 40lb concrete block.
The information on this dinosaur is based on more than 7 complete species that were found in Mongolia. That region is known to be desert like so we know that the Tarchia were desert creatures.
Just for fun we have a soundclip available for you to hear what a Tarchia could've sounded like. Click to the Dinosaur Sounds area to hear it. Please note that the dinosaur sounds are only for entertainment and are not an actual fact.