Imagine that you're a paleontologist examining the fossilized remains of a new genus of dinosaur--a hadrosaur, say, or a gigantic sauropod. After you've figured out how the specimen's bones are put together, and what type of dinosaur you're dealing with, you go on to estimate its weight. One good clue is how long the "type specimen" is, from the tip of its skull to the end of its tail; another is the published weight estimates for comparable types of dinosaurs. If you've discovered a huge titanosaur from late Cretaceous South America, you might venture a guess of 80 to 120 tons, the approximate range of South American giants like Argentinosaurus and Futalognkosaurus.
Now imagine that you're trying to estimate the weight not of a dinosaur, but of an obese stranger at a cocktail party. Even though you've been around human beings all of your life, of all shapes and sizes, your guess is likely to be wildly inaccurate: you might estimate 200 pounds when the person actually weighs 300 pounds, or vice-versa. (Of course, if you're a medical professional, your guess is likely to be closer to the mark, but still off by 10 or 20 percent.) So the question is, if guessing the weight of people is such a challenge, how do you pull off this trick with a dinosaur that's been extinct for 100 million years?
How Much Did Dinosaurs Really Weigh?
As it turns out, recent research has shown that experts may have been drastically overestimating the weight of dinosaurs. Since 1985, paleontologists have used an equation involving various parameters (the total length of the specimen, the length of certain bones, etc.) to estimate the weight of extinct animals. This equation produces reasonable results for smaller mammals and reptiles, but veers away from reality when larger animals are involved. In 2009, a team of researchers applied the equation to still-extant mammals like elephants and hippopotamuses, and found that it vastly overestimated the weight of these creatures.
So what does this mean for dinosaurs? At the scale of your typical sauropod, the difference is dramatic: whereas Apatosaurus (the dinosaur previously known as Brontosaurus) was once thought to weigh 40 or 50 tons, the corrected equation puts this plant-eater at a mere 15 to 25 tons. Sauropods, it seems, were much more slender than scientists have given them credit for, and the same probably applies to plus-sized hadrosaurs like Shantungosaurus and ceratopsians like Triceratops.
Sometimes, though, weight estimates veer off the tracks in the other direction. Recently, paleontologists examining the growth history of Tyrannosaurus Rex concluded that this fierce predator grew much more quickly than was previously believed, putting on as much as two tons per year during its teenaged growth spurt. Since female tyrannosaurs were bigger than males, this means that a full-grown T. Rex female may have weighed as much as 10 tons, two or three tons more than previous estimates.
Dinosaur Weight - The Heavier, the Better
Of course, part of the reason researchers impute these enormous weights to dinosaurs is that this gives their findings more "heft" with the general public. When you're talking in terms of tons, rather than pounds, it's easy to get carried away and attribute a weight of 100 tons to a newly discovered titanosaur, since 100 is such a nice, round, newspaper-friendly number. Even if a paleontologist is careful to tone down his weight estimates, the press is likely to exaggerate the results. People want their dinosaurs to be really, really big!
The fact is, there's still a lot we don't know about how much dinosaurs weighed. The answer depends on other still-unresolved questions, such as what type of metabolisms dinosaurs possessed (weight estimates can be very different for warm-blooded and cold-blooded animals), how fast dinosaurs grew, and what they ate on a daily basis. The bottom line is, you should take any dinosaur weight estimates with a big grain of Jurassic salt, since future developments may result in a vastly slimmed-down Diplodocus.