Experts once thought this ginormous dino lived in water.

A dinosaur the size of a four-story building slowly approaches a coniferous tree in what’s now North America. Stretching up its long neck, the creature rips off pine needles and leaves that few other dinos can reach. This huge plant-eater is Brachiosaurus, and it’s one of the biggest animals that’s ever walked the planet.

Huge herbivore

Roaming Earth between 156 and 145 million years ago during the Jurassic period, Brachiosaurus grew over 80 feet long and weighed more than 28 tons—that’s about as heavy as four African elephants. Why so big? Experts think that Brachiosaurus couldn’t run, so its size might’ve made fierce predators like Allosaurus think that the dino was too big to take down. Another theory suggests that because the plants were difficult to digest, Brachiosaurus and other giant herbivores needed extra-large digestive tracts to process and absorb the nutrients from their food.

This dino’s name comes from the Greek words meaning “arm lizard” because its forelegs were longer than its hind legs—another adaption to help it reach high into the trees. It’s part of the sauropod family: huge plant-eaters with long necks, long tails, and a four-legged stance. Apatosaurus is also a member of this group.

Mistaken habitat

Scientists once thought that Brachiosaurus lived in water. They figured that such a large animal would be too heavy to support itself on land, plus its nostril holes were on top of its skull, sort of like a snorkel.

But experts now know that the pressure of the water would’ve made it impossible for Brachiosaurus to breathe in air. Plus, the nostril holes don't tell us everything about noses: If aliens examined a human skull without ever seeing a face, they might not know that our noses stick out!

Watch Dino Road Trip

Ali and Sean travel back 150 million years to the Jurassic period to get a look at a flying dinosaur called the Anchiornis. Tour guide Simon reveals that this dinosaur actually had feathers!