Why Did Apatosaurus Have Such a Monstrous Tail?

An Apatosaurus grew to a length of 40 feet (12 m) from its snout to the tip of its tail. It weighed as much as 34 tons (30 t). Most of that great weight was right over its legs. Its neck ended in a fairly small head. Without its long, heavy tail it would have tipped over. The blue whale is the largest animal on earth today. In fact it is probably the largest that has ever lived. Supported by salty ocean water an adult blue whale can grow to weigh a stupendous 190 tons (170 t). On land Apatosaurus at 34 tons (30 t) and Ultrasaurus at 152 tons (136 t) could function as exclusively terrestrial animals, supporting their great weighs on their huge legs alone. Brontosaurs not only survived, they flourished by evolving a skeletal structure capable of supporting their enormous bodies. Dynamics of balance, not unlike those applied to a suspension bridge, supported the heavy body between a long neck and tail. Even so their bulk kept brontosaurs firmly among the plodders and well out of the ranks of the small, more active herbivores and the highly active predatory carnivores of the time. But they all died at the same time.