Discovered in the Yixian formation in north-eastern China, all 31 fossilised dinosaurs were members of a herbivore species called Psittacosaurus lujiatunensis. This fossil specimen was originally described in 2004, but researcher Brandon Hedrick of the University of Pennsylvania in Philadelphia was inspired to investigate it further after seeing a photo of the find.
Hedrick and his colleagues found that the gathering of young dinos was preserved in such exceptional detail by being suddenly engulfed in material flowing from an erupting volcano. The lack of heat damage on the fossilised bones suggests that this flow was a slurry of water, rock and other debris, rather than lava.
Judging by the size of its skull, the older dinosaur was probably around 4 or 5 years old. This species is not thought to have reproduced until it was 8 or 9 years old, so it seems likely that this older companion was not the parent of the infants it was found with. Hedrick’s team believe this could be evidence of babysitting, a behaviour also seen in some modern-day birds.