The oldest known dinosaur nests have been found at the same South African park where scientists previously unearthed the oldest known dinosaur embryo (pictured), a new study says.
Paleontologists recently found ten nests—each containing several tightly clustered eggs—in a nearly vertical cliff in Golden Gate Highlands National Park. Both the nests and the previously discovered embryo date back 190 million years.
The new find shows that the region was an early Jurassic nesting site used by a plant-eater called Massospondylus carinatus. The site predates other known dino nesting grounds around the world by more than a hundred million years, scientists reported this week in the journal Proceedings of the National Academy of Sciences.
After the ancient fossil embryo was described in 2005 (pictures), "we decided to go back to the original site and see if we [could] find embryos and nests in place in the rock wall," said study co-author Robert Reisz, a vertebrate paleontologist at the University of Toronto in Mississauga.
"After a lot of searching and walking on hands and knees and crawling ... we found a total of ten nests altogether in locality, which is amazing."
A Massospondylus parent cares for its young in an artist's rendering.
The newfound dinosaur-egg clutches provide the oldest evidence yet for several aspects of dinosaur behavior, according to the study.
For example, paleontologists found multiple nests in a single layer of rock, suggesting that mothers gathered in groups to lay their eggs. This is the oldest example of "colonial nesting" in the fossil record, the scientists say.
One of the newfound egg clutches contained 34 eggs (pictured), which were likely submerged during a flood. The shells' extreme thinness—only about a hundred microns wide—made them hard to spot, Reisz noted.
Eggs in the clutches were arranged in single layers, meaning a mother dino must have created a "controlled nesting environment" by possibly organizing the eggs, he added.
The scientists were also surprised to find several generations of nests in different levels of rocks, suggesting the dinosaurs regularly returned to the same site to lay their eggs.
An egg clutch recovered from the South African site in 1976 (pictured) had two exposed skeletons, including the embryo in the first picture of this gallery, which wasn't formally studied until 2005. These embryos have since given scientists valuable insights into dinosaur evolution.
For example, the Massospondylus embryo resembles "a dwarf version of a sauropod dinosaur," the largest animals to walk the Earth, Hans-Dieter Sues, a paleontologist at the National Museum of Natural History in Washington, D.C., said in 2010. (See a sauropod picture.)
This means that Massospondylus had characteristics that "foreshadowed" the look of sauropods, which evolved later, he said.