The mystery of the Tyrannosaurus Rex may have been solved. We take a look at the mystery of the Tyrannosaurus Rex. This giant predator lived during the cretacous period from 83 million to 66 million years ago. The Tyrannosaurus rex was one of the largest carnivorous dinosaur that ever lived, it measured up to 43 feet long and weighed as much as 7 tons. One thing the t rex is known for is it's small arms. Paleontologists studying them have said that due to their size they wouldn't have been very useful. It's thought though the arms were small in regards to the rest of the body because they simply weren't needed. The bite of this predator was so powerful they didn't need any extra help. Even though they were small it's still believed there arms were quite muscular and were able to bench press around 400lbs each. Thank you for watching! Thank you to CO.AG for the background music!