In the French village of Plagne, in the Jura Mountains, 200 kilometers east of Lyon, there is a set of huge footprints made 150 million years ago. The footprints belonged to a sauropod, the largest class of dinosaurs, that had very long necks, which helped them reach the foliage on top of tall trees, long tails and four thick, pillar-like legs. An adult sauropod easily weighed 100 tons, although this particular individual probably weighed about 35 tons.