Scientists estimate that the largest known sauropod's bones belonged to animals that weighed about 80 tons. Length is harder to estimate, the scientists say, but some stretched at least 100 feet from head to tail.
University of Pennsylvania paleontologist Peter Dodson said there was only one mammal that ever rivaled it for size, a giant rhinoceros that weighed about 20 tons. But that animal died out relatively quickly and became an evolutionary dead end.
Most people don't appreciate the sheer size of the sauropods because these creatures are so hard to reconstruct and their skeletons wouldn't fit into most human-scale buildings, said Don Lessem, a local collector and dinosaur enthusiast who has put together a new exhibit, opening Sunday at the Franklin Institute.
Lessem said this exhibit will be based on the latest dinosaur science but will be accessible to children, dealing with such burning questions as what kind of giant cowpies, or sauro-pies?, littered the Jurassic forest floor.
Why did they grow so big? Martin Sander, a paleontologist at the University of Bonn, said the main reason that animals grow to any particular size is to fill a niche. For sauropods, there was room at the top.
By being big, sauropods could eat leaves and branches too high for other creatures to reach, said Sander, who is acting as an adviser to the exhibit. And with predators such as T. rex around, size probably helped their chances of survival.
As a general rule, big herbivorous animals grow about 10 times as massive as the largest predators. Elephants are about 10 times the mass of lions and sauropods were about 10 times the size of T. rex.
