An individual T-rex had a lifespan of just under 30 years. The T-rex species appeared about 68 million years ago (mya) and lasted until 65.5 mya. That means that the T-rex existed for 2.5 million years.
T-Rex is the short form on Tyrannosaurus. The first T-Rex appeared on earth during the early Cretaceous about 137 million years ago. "T-Rex" means the king of the dinosaurs. They were carnivorous and mainly eat smaller dinosaurs.
I think the T-Rex Demuniacx's Answer: The T-rex was in the upper/late cretactuos period.In the carbiniferous period which was about a couple million years between both periods has the answer to the first dinosaur. The Arthropleura.