For 140 million years, sauropods roamed Earth--but today we have just fossils to tell us about what these animals looked like from the outside. How big were they? How big were their young? What did their skin look like? How fast could they move? And while fossils can't answer every question--like what color the animals were--they do reveal an astonishing amount of information that helps paleontologists understand these massive creatures.
All dinosaurs reproduced by laying eggs, just as living birds and many modern reptiles do. But surprisingly, the babies that hatched out of sauropod eggs were generally no bigger than a modern adult goose. Sauropods didn't start out extremely big--they just grew very, very fast.
As amazing as it seems, we have footprints of sauropods on nearly every continent, left during their 140-million-year stint on Earth. And those footprints, many in long trackways, provide some of the best data on the animals' daily life. With them, scientists can tackle such questions as: How fast could these animals walk? Did they travel in groups? Did young and old move together?
Sauropods came in different sizes--most of them big. An adult female Mamenchisaurus would have weighed about 13 tons (12,000 kilograms). That may sound big, but it's actually below average for sauropods.
In humans, skin is the biggest organ--an average adult's skin weighs as much as a gallon of milk. The skin of an adult Mamenchisaurus weighed about as much as a small car.