What Was the Biggest Dinosaur? The Titanosaurs That Outweighed Planes

Imagine an animal so long that it would cover more than a third of a football pitch. So heavy that it weighed as much as ten African elephants. These giants were real, and they walked across what is now Argentina about 100 million years ago.

The titanosaurs

The biggest dinosaurs belonged to a group of sauropods, the long-necked, long-tailed plant-eaters that walked on four pillar-like legs. Among sauropods, the largest of all were the titanosaurs, most of which lived in the Southern Hemisphere during the Cretaceous period.

Patagotitan mayorum was found on a farm in Patagonia in 2012. The bones of at least six individuals were excavated, and in 2017 a team led by José Carballido formally described it. They estimated it was about 37 metres long and, using the thickness of its thigh bone and upper arm bone, weighed around 69 tonnes, with other methods giving somewhat lower values.

Argentinosaurus, described in 1993, is known from far fewer bones: some vertebrae, ribs and part of a leg. Its vertebrae alone are taller than a person. Estimates for its size are similar, around 35 metres and 60–80 tonnes, and it may have been as big as or bigger than Patagotitan.

Why the numbers are uncertain

No complete skeleton of a giant titanosaur has ever been found. Scientists estimate their size by comparing the bones they have with more complete relatives and by measuring the circumference of the thigh and upper arm bones. In living four-legged animals, the thickness of these bones is closely linked to body weight, because they carry the load. Different methods can give results that differ by tens of tonnes, so claims about the “biggest dinosaur ever” change as new fossils and techniques appear.

How did they get so big?

A major 2011 review led by palaeontologist Martin Sander looked at why sauropods, and only sauropods, reached such sizes on land. Several features worked together:

• Air-filled bones. Like birds, sauropods had air sacs connected to their lungs, which extended into their vertebrae. That made the skeleton much lighter and their breathing very efficient.
• A long neck. Standing still and sweeping its head over a wide area, a sauropod could reach huge amounts of food while spending little energy walking.
• No chewing. Sauropods stripped leaves and swallowed them whole, leaving digestion to their enormous guts. A small head without heavy chewing teeth made a long neck possible.
• Eggs and fast growth. Sauropods laid many small eggs and grew extremely fast. Unlike large mammals, they did not need years of pregnancy and parental care, so populations could recover quickly.

Bigger than a whale?

Titanosaurs were longer than any animal alive today, but probably not heavier than the biggest of all. The blue whale can reach about 30 metres and is thought to weigh well over 150 tonnes. Water supports its body, which allows a much greater mass than would be possible on land. The blue whale may be the heaviest animal that has ever lived.

In short

• The biggest dinosaurs were titanosaurs, long-necked plant-eaters from South America.
• Patagotitan was about 37 metres long and roughly 60–70 tonnes.
• Argentinosaurus may have been similar in size, but is known from fewer bones.
• Size estimates rely on bone measurements and comparison with relatives, so they are uncertain.
• Air-filled bones, long necks, swallowing without chewing and fast growth made giants possible.
• The blue whale is shorter but probably much heavier than any dinosaur.