In the Cretaceous period over a hundred million years ago, Argentina's Sanagasta Valley was alive with hydrothermal activity, much like Yellowstone National Park or Iceland are today. Tunnels of near-boiling, mineral-rich water crisscrossed the subsurface (figures below, from the paper), and explosive geysers pockmarked the landscape. Doesn't seem like a very inviting place to raise a family.
But researchers found some 80 clutches of fossilized eggs in the area, many of them containing a dozen or more eggs each. Even more strange, the nests were almost exclusively found within 10 feet of a geyser or hot spring. It seems that far from avoiding the hydrothermal features, dinosaurs were purposefully laying eggs near them as a way to keep them incubated during their 1-2 month long gestation.
