Some 66 million years ago, a Tyrannosaurus rex weighing an estimated 19,555 pounds—nearly as much as four pick-up trucks—roamed what is now the Canadian province of Saskatchewan. Measuring roughly 42 feet long, the dinosaur led what University of Alberta paleontologist Scott Persons describes as an “unusually long” but violent life, enduring injuries ranging from broken ribs to an infected jaw before dying in its early 30s.
Researchers first unearthed the formidable T. rex’s remains in 1991, Michael Greshko reports for National Geographic. Given the dinosaur’s sheer size and encasement in cement-like sandstone, however, it took more than two decades to fully excavate and analyze the bones. Luckily, the paleontologists behind the find write in the Anatomical Record, the results were worth the wait: Not only is the T. rex, nicknamed “Scotty” in honor of a celebratory toast of scotch raised upon its discovery, the biggest member of its species ever found, but it also holds the distinction of being the longest-lived T. rex identified in the fossil record to date.
"This is the rex of rexes," study lead author Persons observes in a statement. “There is considerable size variability among Tyrannosaurus. Some individuals were lankier than others and some were more robust. Scotty exemplifies the robust.”
To gauge Scotty’s size, Persons and his colleagues measured its leg, hip and shoulder bones. According to Gizmodo’s George Dvorsky, although the dinosaur’s skeleton is only 65 percent complete, the team was able to estimate its body mass by using the circumference of the femur to calculate the amount of weight the legs could withstand.
Compared to 11 similarly well-preserved T. rex skeletons, Scotty appears to have the advantage in terms of pure mass, if not height and overall length. Sue, a dinosaur unearthed in 1990 and the previous biggest T. rex record holder, weighed an estimated 18,651 pounds, or some five percent lighter than the new heavyweight title winner.
Still, it’s worth pointing out that “biggest dinosaur” is a fairly imprecise measure. As Brian Switek explains for Scientific American, “biggest” could refer to weight, length or a combination of the two. Switek writes:
Given all sorts of variations, it’d be possible for two T. rex to have exactly the same length but have different weights—or have different weights at varying lengths—in which case awarding a superlative title becomes subjective.
Switek further notes that Scotty’s skeleton is far less complete than Sue’s, which remains around 90 percent intact. John Hutchinson, an evolutionary biomechanics expert from the University of London’s Royal Veterinary College who was not involved in the new research, tells Gizmodo’s Dvorsky that Scotty is not “appreciably larger than other known specimens.” Instead, Hutchinson says, the difference is at best five percent, “and that is with a wide margin of error.” In all, Switek says, Scotty and Sue likely stood within just a few ounces and inches of each other.
Regardless of Scotty’s exact place in the T. rex lineage, it remains impressive for its longevity and seemingly battle-worn lifestyle. At some point in the dinosaur’s 30-year or so existence, it encountered enemies that inflicted such injuries as an infected jaw, an impacted tooth and broken ribs. Damage evident on Scotty’s tail vertebrae also indicates it was bitten by a fellow T. rex.
It’s probably no coincidence that Scotty was both enormous and long-lived: Roni Dengler of Discover magazine writes that the dearth of similarly sized T. rex fossils suggests most of the dinosaur’s peers didn’t survive long enough to reach their full potential.
As Persons concludes to Dengler, “Scotty has pushed the envelope of how big we now know T. rex was.”