Everybody likes a good soak in a hot bath from time to time. But new research suggests that some dinosaurs took it to the extreme, laying their eggs in the steaming hot soils near hot springs and Old Faithful-like geysers in what is now northwestern Argentina.
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.
Gerald Grellet-Tinner of the Field Museum in Chicago and Lucas Fiorelli of CRILAR in Argentina published their findings in the journal Nature Communications.
So far, the scientists are still uncertain what species of dinosaur laid the eggs; no bones have been found that can be linked directly to the eggs. But the eggs are enormous -- over eight inches in diameter, bigger than an ostrich egg (figures at left, from the paper) -- and bones found in the region belong to the Titanosaur family, 100-ton beasts that are among the largest animals to ever walk the planet.
Grellet-Tinner and Fiorelli think the nesting site was chosen because the consistent heat would be a good way to ensure such large eggs remained warm.
Interestingly, the eggshells also varied a lot in thickness, between 1.29 and 7.94 millimeters (.05 and .31 inches) thick. By contrast, chicken eggshells are around .311 millimeters thick. The researchers believe that all healthy eggs would have been on the thicker end of the spectrum at first, an evolutionary adaptation designed to prevent them from being destroyed while they spent weeks marinating in hydrothermal acids (which explains the thinner shell piece):
...we hypothesize that the 7-mm thick eggshells offered an adaptation to chemical dissolution in an extreme environment by buffering external erosion from acidic hydrothermal fluids, thus providing sufficient time for embryonic development.
If so, that would mean these particular dinosaurs had a unique dependence on hydrothermal vents for survival. The heat and moisture from geyser activity were more than just convenient; they were crucial parts of the dinos' reproductive cycles, incorporated into their nesting instincts and the architecture of their eggs over generations.
It's unlikely that all -- or even most -- dinosaurs sought out such harsh conditions to lay their eggs. But the researchers note that though the discovery is the first of its kind, it may not be the last example we find that dinosaurs relied on Earth' primordial heat to survive and procreate.
Images: Nature Publishing Group
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