Three large Alamosaurus dinosaurs in a forest. One is eating the leaves at the top of a tree. Pterosaurs are flying around them. — The biggest dinosaurs in the world were titanosaurs. In fact, these prehistoric reptiles are the largest land-dwelling animals that have ever existed. © Herschel Hoffmeyer/ Shutterstock

What was the biggest dinosaur?

By Emily Osterloff

Some dinosaurs could reach enormous sizes. In fact, the very biggest would tower over any land animal alive today!

Get to know some of the largest dinosaurs to have ever walked the planet.

How do we know how big dinosaurs were?

Dinosaur size estimates often need to be taken with a pinch of salt.

It’s one thing to work out how long a dinosaur was when you have a relatively complete skeleton. It’s a trickier task when you’ve only got a few bones to work with.

“The only way you can really do it is to find a closely related dinosaur that we know the whole skeleton of and assume the proportions are the same,” explains our palaeontologist Dr Susie Maidment. “But just because they’re closely related doesn’t mean the tail or neck were the same length, or they might have been taller – it isn’t straightforward.”

Then there’s mass. How much a dinosaur weighed can be estimated in a couple of ways.

For example, in living quadrupeds if you add together the circumference of the humerus, which is the upper arm bone, and femur, which is the thigh bone, the result is directly proportional to the animal’s mass. In theory, this means that if you had the limb bones of a dinosaur, you could calculate how much it weighed.

But the largest animals we’re certain this method works for are six tonne African elephants. The biggest dinosaurs may have been ten times heavier.

“There might be questions over how valid those extrapolations are,” says Susie. “The error bars are also extremely large. We did this for Sophie the Stegosaurus and we ended up with a body mass of anywhere between 1.5 and six tonnes, which is a very big difference.”