Lythronax is a very recent discovery. This tyrannosaur measured over 26-30 feet in length and weighed over 2-3 tons. Lythronax may have the most fear inspiring name of all dinosaurs. It's full name, Lythronax argestes, means the gore king of the south. Lythronax really was a king. It was the largest predator in it's environment and would have been at the top of the food chain. Lythronax lived about 80 million years ago in North America.