There are big dinosaurs. There are old ones. And then there is Scotty, a giant among them all.

A Tyrannosaurus rex found in Saskatchewan, Canada, in the 1990s is the heaviest and oldest of its kind, paleontologists recently announced. The dinosaur, nicknamed Scotty, probably weighed about 9.8 tons and lived for more than three decades, they said. The results were published in a study last week in The Anatomical Record, a scientific journal, and posted online.

“This is the rarest of rare dinosaurs,” Gregory Erickson, a paleobiologist from Florida State University who was one of the study’s authors, said in an interview Wednesday. “We have a full, grown adult.”

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Researchers estimated Scotty’s weight by measuring its hip, leg and shoulder bones, and comparing them to the skeletons of other T. rex specimens. The size and width of the femur bone suggest Scotty weighed 19,555 pounds, much larger than a male African elephant, which can grow to 14,000 pounds. In May, a new, updated cast of Scotty, which will reflect the scientists’ findings, will go on display at Royal Saskatchewan Museum in Regina, the capital of Saskatchewan.