Brontosaurus
"Brontosaurus" was a large, long-necked quadrupedal animal with a long, whip-like tail, and forelimbs that were slightly shorter than its hindlimbs. The largest species, "B. excelsus", weighed up to and measured up to long from head to tail. For comparison, the current largest land animal, the average male African bush elephant is 3.20 m (10.5 ft) tall at the shoulder and has a body mass of 6,000 kg (13,228 lb) or 6.6 short tons.
Brachiosaurus
Most estimates of "Brachiosaurus altithorax" size are based on the related African brachiosaurid "Giraffatitan" (formerly known as "Brachiosaurus brancai"), which is known from much more complete material than "Brachiosaurus". The two species are the largest brachiosaurids of which relatively extensive remains have been discovered. There is another element of uncertainty for the North American "Brachiosaurus" because the type (and most complete) specimen appears to represent a subadult, as indicated by the unfused suture between the coracoid, a bone of the shoulder girdle that forms part of the shoulder joint, and the scapula (shoulder blade). Over the years, the mass of "B. altithorax" has been estimated at , , , , , and . The length of "Brachiosaurus" has been estimated at 20–21 meters (66–69 ft) and , and its height at and 12–13 meters (39–43 ft).