Brachiosaurus dinosaurs. Artwork of three Brachiosaurus dinosaurs feeding at night in a moonlit forest of trees and ground-growing ferns. Brachiosaurus was the tallest dinosaur, standing up to 16 metres tall. It could weigh up to 70 tons. Unusually for a dinosaur, its front legs were longer than its hind legs. It was herbivorous, probably feeding on leaves high in the trees. It lived in the late Jurassic period, between 155 and 145 million years ago. It is thought to have been a social animal, living in herds.