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.
Ankylopollexia
Primitive ankylopollexians tended to be smaller as compared to the larger, more derived hadrosaurs. Of course, there are exceptions to this trend. A single track from a large ornithopod, likely a relative of "Camptosaurus", was reported from the Lourinhã Formation, dating to the Jurassic in Portugal. It had an estimated hip height of around , nearly a metre larger than the holotype femur of contemporary relative "Draconyx", estimated by the authors to be in weight. The primitive styracosternan "Iguanacolossus" was named for its distinct robustness and large size, likely around in length. Regarding hadrosaurs, one of the more basal members of Hadrosauroidea, the Chinese genus "Bolong", is estimated to have been around . Another exception of this trend is "Tethyshadros", a more derived genus of Hadrosauroidea. Estimated to have weighed , "Tethyshadros" have been found only on certain islands in Italy. Its diminuitive size is explained by insular dwarfism.