All dinosaurs start off life small. That’s as true for today’s birds as the titans of the Mesozoic, and it may have been a critical part of what allowed ancient dinosaurs to surpass mammals in size. In order to hatch and grow into such stupendous shapes, though, the little egg-bound dinosaurs had to be nestled in a cozy little refuge. How did the biggest of the big care for their incubating little ones?
The classic image of a dinosaur on its nest is “Big Mamma.” Surrounded by elongated eggs, arms outstretched to protect them, the dinosaur was a model parent, even to the death. But this strategy wouldn’t have worked for huge, multi-ton dinosaurs, particularly the long-necked sauropods. These giants must have done something else to keep their broods safe and warm, and, according to paleontologist E. Martín Hechenleitner and colleagues, the solution may have anticipated what some modern dinosaurs do.
Nests of sauropod dinosaurs—particularly a subgroup called titanosaurs—have been found in Europe, Asia, India, and South America. These usually aren’t isolated finds. The giant dinosaurs congregated in vast nesting grounds, much like their ancestors did back at the dawn of the Jurassic. After digging out a nest, perhaps with the claws of their hind feet, the gravid dinosaurs squatted down to deposit their rounded eggs into the depression.
Titanosaurs didn’t just pick any old spot to lay their eggs, though. In Sanagasta, Argentina, for example, the dinosaurs chose to nest in a place dotted by active geothermal features that recall the geyser basins of Yellowstone—a natural source of heat—and an aggregation of 75 nests at another site in Spain suggests that titanosaurs were drawn to special spots on the landscape. And at locales where there wasn’t built-in heat, such as a nesting site in France, the dinosaurs may have collected decaying plant material to build mounds over their precious eggs.
If this sounds at all familiar, it’s because some modern birds use some of the same strategies. Megapodes, turkeys that live throughout Australasia, don’t sit on their nests, but find other ways to keep their eggs at their required temperature. For instance, Hechenleitner and coauthors write, the Malau megapode scratches nests over six feet deep into the soil to lay its eggs close to a source of geothermal heat. And while fossils of organic nest material have yet to be found at titanosaur nest sites, the microstructure of the eggshells and comparisons to the modern megapodes hint that some of the huge dinosaurs may have buried their eggs in mounds just like their living cousins do.
The titanosaurs probably weren’t model parents. The general view, at least at the moment, was that they were “lay ’em and leave ’em” dinosaurs, not providing anywhere near the care provided by Littlefoot’s mom. But neither were they dumb brutes that plopped eggs down wherever. Titanosaurs were picky dinosaurs that used the environment to raise their offspring during the critical early days. Watch a megapode scratched into the warm soil, and you’re seeing a glimmer of the Mesozoic moments that continued the dinosaurian reign for millions upon millions of years.
Fowler, D., Hall, L. 2011. Scratch-digging sauropods, revisited. Historical Biology. doi: 10.1080/08912963.2010.504852
Hechenleitner, E., Grellet-Tinner, G., Fiorelli, L. 2015. What do giant titanosaur dinosaurs and modern Australasian megapodes have in common? PeerJ. doi: 10.7717/peerj.1341