Even though they grew to be some of the largest animals ever to walk the earth, sauropod dinosaurs started off small. From numerous nesting sites found all over the world it appears that gravid female sauropods, rather than putting all their effort into laying a few enormous eggs, created large nests of numerous, relatively small eggs. But why they selected particular nesting sites has long been a mystery. Now, in the journal Nature Communications, paleontologists Gerald Grellet-Tinner and Lucas Fiorelli provide evidence that nesting female sauropods picked at least one site based upon its natural heat.
In northwestern Argentina's La Rioja Province lies a bed of white Cretaceous rock called the Los Llanos Formation. Within that formation, paleontologists have found numerous clutches of eggs at Sanagasta. The eggs are very similar to those of sauropod dinosaurs found elsewhere in Argentina, but the focus of the new study is not so much the eggs as the environment they were deposited in. In one particular area, designated sub-site E, the egg clutches are found dispersed three to ten feet away from geysers, vents, and other hydrothermal features which were active between 134 and 110 million years ago—that is, the eggs were laid in a naturally-heated nursery incubated between 140 and 212 degrees Fahrenheit. During the time the dinosaurs occupied this site, it must have looked somewhat reminiscent of some areas of Yellowstone National Park, but with sauropods wandering among the hot springs instead of elk and bison.
Although this is a wonderful discovery, the fact that these dinosaurs came back to the hydrothermally-active site again and again is not unusual. Some ground-nesting birds, such as the Polynesian megapode, seek out sites warmed by volcanic activity to create their nests, and so it seems that sauropod dinosaurs, too, were very selective about where they created their nests. With this in mind, paleontologists can take a closer look at other nesting sites around the world for clues as to why certain sites were "hot spots" for dinosaur nests.
For more on this discovery, see Not Exactly Rocket Science and Nature News.
Gerald Grellet-Tinner & Lucas E. Fiorelli (2010). A new Argentinean nesting site showing neosauropod dinosaur reproduction in a Cretaceous hydrothermal environment. Nature Communications, 1-8 : 10.1038/ncomms1031