T-rexes are considered to be the most ferocious predators that lived about 68 million years ago in the western part of North America. Recent research suggests that they outcompeted the adults of smaller species. Fossil specimens show that a T-rex dinosaur weighed about 8 tonnes (8000 kg), could be up to 12 metres long (40 feet) and 6 metres high (20 feet). The growth rate of these dinosaurs with a life span of not more than 28 years, was very high. They reached their adult size by teenage. It has also been found that the average size of their jaw was 1.2 metres and they could consume about 230 kg of meat in one bite.