August 2, 2024 — When picking a random person out of a crowd, it’s statistically improbable that they would be the tallest human ever. The same principle applies to dinosaurs. Of all the Tyrannosaurus rex fossils discovered, it is unlikely any are the largest of their species.
A recent study estimates that the largest T. rex could have been 70 percent more massive than the largest specimen currently on record. This would mean a colossal weight of around 15,000 kg (30,000 pounds), compared to the largest known T. rex, “Scotty,” who weighed about 8,800 kg.
Paleobiologist Jordan Mallon from the Canadian Museum of Nature and paleontologist David Hone from Queen Mary University of London tackled the issue many scientists face: estimating the size range of a species based on a limited number of specimens.
The study highlights that, without extensive sampling over different times and locations, establishing the upper limits of body size for a species, even one that is still extant, is challenging.
Filling Gaps with Virtual Models
Given that approximately 2.5 billion T. rexes roamed the Earth over a span of 2.4 million years, the current dataset of 84 reasonably complete skeletons is rather small. To address this, Mallon and Hone generated 140 million virtual T. rex individuals using a computer model. This model assigned body mass based on various factors, including population size, growth rate, lifespan, and gaps in the fossil record.
Their analysis suggests that the largest T. rex specimens we have discovered are larger than 99 percent of all T. rexes that ever lived. However, the curve’s steepness in the final 1 percent remains uncertain.
Using Modern Relatives as Reference
To estimate the size variation of adult T. rexes, the researchers used the American alligator (Alligator mississippiensis) as a reference, due to its close evolutionary relationship. This approach is not perfect, but it helps to approximate sizes of different sexes within the species.
While the study focuses on T. rex, the implications extend to all dinosaur species and many other fossil organisms. Mallon and Hone emphasize that comparing size statistics is more meaningful than comparing individual skeletons.
“It’s important to stress that this isn’t really about T. rex, which is the basis of our study, but this issue would apply to all dinosaurs, and lots of other fossil species,” says Hone. “Arguing about ‘which is the biggest?’ based on a handful of skeletons really isn’t very meaningful.”
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