Babysitting isn't a human invention: roughly 3% of mammal species, and 8-9% of modern bird species, involve individuals other than the parents in raising the young. And this fossil nest, found in the Cretaceous rocks of Liaoning Province, China, might be the first known example of dinosaur babysitting.
Researchers from the University of Pennsylvania, working with a team from the Dalian Museum of Natural History, identified the skeletal remains of 24 infant Psittacosaurus, and one subadult of the same species. As the subadult (4-5 years) was likely not yet old enough to reproduce, the researchers speculate that it may have been acting in a babysitter-type role . . . possibly an older brother or sister helping its parents out with their latest clutch.
Things ended poorly for all 25 Psittacosaurus, as the entire group was buried alive in a fast-moving volcanic mudslide. Not one of history's most successful babysitters (assuming that's what was happening here in the first place . . . it's still possible that this wasn't a nest at all, but a post-mudslide assemblage of victims that didn't associate in life.)
Photo taken from University of Pennsylvania press release.