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About 66 million years ago, a Tyrannosaurus rex walked the lands of central Canada. This dinosaur was massive. It weighed about 19,500 pounds, almost as much as two elephants. It was about 42 feet long, about the length of a semi-trailer truck.

Scott Persons is a paleontologist. He studies fossils, the remains of living things from long ago. Persons said the notably huge T. rex lived a long but tough life. It experienced many injuries before dying in its early 30s.

Scientists first found the T. rex's remains in 1991. They nicknamed the fossil "Scotty." It took more than 20 years to fully dig up and study Scotty's bones. That was because of the dinosaur's huge size, plus the fact that the fossils were stuck in cement-like stone.

The results were worth the wait, according to Persons. He led a recent study to determine the fossil's size. Persons and his fellow scientists say Scotty is the biggest T. rex ever found. They also believe it lived of longest life of any T. rex ever found.

"This is the rex of rexes," Persons said. He pointed out that T. rexes could vary in size. Some were thinner. Others were more stocky. Scotty was a stockier T. rex.

To figure out Scotty's size as a living dinosaur, Persons and his coworkers measured the fossil bones. Not all of Scotty's bones were found. The scientists think they have about 6 out of every 10 bones from Scotty's body, or 65 percent. Still, the scientists were able to estimate Scotty's weight.

To do so, they measured the thickness of the leg bones. They used this to make an informed guess about how much weight they could hold.

Compared with 11 similar T. rex skeletons, the scientists say Scotty is the biggest by weight. He has taken this title from Sue, a T. rex found in 1990. Sue was believed to weigh about 18,500 pounds. That is about 1,000 pounds less than Scotty.

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