What Were the Largest Dinosaurs Ever?

For many decades, king among the largest dinosaurs known was Brachiosaurus, a large sauropod. This dinosaur reached heights of 15 m (48 ft) and could be as long as 28 m (92 ft). It weighed about 50 tonnes. Based on its huge size, it probably didn't have any predators. Brachiosaurus is no longer the largest known dinosaur, but it is among the largest dinosaurs known from a complete skeleton. Unlike many other sauropods, Brachiosaurus had a giraffe-like build that would have let it reach the leaves of the tallest trees. Like other sauropods, Brachiosaurus had a barrel-shaped abdomen, erect limbs, and was herbivorous. It would have towered over the largest dinosaurs that were predatory, such as theropods like T. Rex.

The length of time it took for a Brachiosaurus to grow to full size would vary depending on whether it was warm or cold-blooded -- if it was warm-blooded, it would have taken about 10 years to grow to full size, and if cold-blooded, 100 years. Many scientists believe that dinosaurs were somewhere in between the warm and cold-blooded animals of today, with a metabolism elevated for a reptile but slow compared to mammals. To grow to adulthood, the dinosaur would have needed to consume about 182 kg (400 lb) of food per day. The largest dinosaurs benefited from their bulk, which would have been effective at retaining heat and keeping the animal's metabolism elevated.

Believe it or not, there were other sauropods bigger than Brachiosaurus. One genus, Giraffatitan, is a couple meters taller than Brachiosaurus, to which it was closely related. Other "brachiosaurids" appear to have been larger or heavier than Brachiosaurus, including Argentinosaurus and Supersaurus. One brachiosaurid, Sauroposeidon, whose name means "earthquake lizard-god," was as tall as 17 m (56 ft), making it the tallest and one of the largest dinosaurs known. Sauroposeidon probably weighed as much as 60 tonnes, 20% more than Brachiosaurus.

Another dinosaur, Bruhathkayosaurus, whose name means "huge bodied lizard," is thought to be the heaviest dinosaur that ever lived. It is controversial, however, as the remains are fragmentary and have not been properly described. If the initial estimates are correct, the species weighed as much as 175-220 tonnes. It could have even been heavier than the blue whale, which weighs 180 tonnes. This large-bodied dinosaur is not the largest (although it was huge), but thought to be the heaviest, because of its fat body.