What was the biggest dinosaur?

We tend to think of most dinosaurs as big, but sauropods are the real heavyweights. This is the group that includes Diplodocus, and dinosaurs in this category tend to have long necks and tails, tiny heads and massive bodies. They first appeared around 200 million years ago in the Late Triassic or Early Jurassic periods.

Most of the heaviest sauropods belong to a group call titanosaurs. Until quite recently, their fossil remains were sparse. However, starting around two decades ago, a treasure trove of titanosaurs has been unearthed in Argentina. First, in 2000, came Futalognkosaurus, and eventually they amassed around three quarters of an entire skeleton from three specimens. In 2005, they found the Dreadnoughtus, which is even bigger. But the most astounding discovery came in 2013 when six specimens of a truly humungous beast, Patagotitan, started to emerge from the ground.

Since Patagotitan was discovered, it has often been described as the largest animal ever to walk the earth. However, estimating the weight of these dinosaurs is not straightforward. Recent analyses – one using computer-generated models and the other based on clay models – are in broad agreement. They put Futalognkosaurus at around 29 tonnes and Dreadnoughtus at about 31 tonnes. Patagotitan comes in at a whopping 55 tonnes, which is ten times the mass of an elephant, the largest living land animal.

But the story doesn’t end there. A reappraisal of an almost legendary dinosaur found in 1878 suggests it might have been twice as heavy as Patagotitan. The estimate is contentious, being based on a single fragmentary vertebra – spine bone – that has since been lost. But if correct that it would make Amphicoelias fragillimus, at between 80 and 120 tonnes, by far the heaviest land animal we know of.