If you randomly pick someone from a crowd, they likely won’t be the tallest person who ever lived. The same logic applies to dinosaurs.
Given the Tyrannosaurus rex fossils we’ve found, it’s statistically improbable that any of them represent the largest individual of their species. Determining their exact size range is challenging.
A recent study suggests that the largest T. rex might have been 70% heavier than the largest specimen on record. This hypothetical T. rex could have weighed around 15,000 kg (30,000 pounds), compared to Scotty, the largest known fossil, which is estimated to have weighed 8,800 kg.
Paleobiologist Jordan Mallon from the Canadian Museum of Nature and paleontologist David Hone from Queen Mary University of London explore the difficulties life scientists face when estimating a species’ size range from a limited sample.
As the researchers state, “unless population sampling is both intensive and spatiotemporally exhaustive, it can be difficult to establish the upper limits of body size even for extant species.”
An estimated 2.5 billion T. rexes lived during their brief 2.4 million-year existence, yet we have only 84 reasonably complete skeletons. “Some isolated bones and pieces certainly hint at still larger individuals than for which we currently have skeletons,” says Hone.
To bridge the gaps, Mallon and Hone created 140 million virtual T. rex models using a computer program that assigns body mass based on variables like population size, growth rate, lifespan, and fossil record gaps.
This modeling helped estimate the relative sizes of known fossil specimens, suggesting we’ve likely found a T. rex larger than 99% of all others that ever lived. The final 1% remains uncertain.
The T. rex was chosen because it’s a well-documented species with many estimated variables. However, we know little about T. rex’s adult body size variation, so the researchers used the American alligator (Alligator mississippiensis), a close relative, as a reference for different sex sizes.
While not perfect, this model predicts a dinosaur 70% larger than Scotty. However, the authors caution that the 15,000 kg estimate is more theoretical than a confirmed size any T. rex reached.
Further research into T. rex sexual dimorphism and biomechanical and ecological constraints could provide clearer insights.
Mallon and Hone’s research highlights the importance of comparing statistics rather than individual skeletons when discussing the largest dinosaurs. “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.”