"We know there wasn't time for scavengers to come and pick at the carcasses," he said.
Scientists study the death assemblages of species to learn more about how the animals behaved while alive.
The close proximity of the Psittacosaurus fossilsthe adult and juvenile skeletons were all located within half a square meter (5.4 square feet)points to a biological relationship and post-hatching parental care.
The hatchling size of the Psittacosaurus is not known. But the juvenile bones found were wellformed and fully hardened, or ossified. The youngsters' apparently healthy state suggests the adult had cared for its children.
"Recognizing parental care in the fossil record has been difficult in the past, because behavior isn't typically discernable from a single time-slice," said Jeff Wilson, a paleontologist at the University of Michigan in Ann Arbor.
"This specimen is a rare snapshot of a momentthe last momentin these dinosaurs' lives and shows them clustering around an adult. I think that is a compelling case that there was a strong bond between these animals," he said.
Past studies have suggested that other dinosaur species displayed parental care by, for example, feeding their children. But researchers were not sure if such behavior extended to all dinosaurs.
"This suggests maybe all dinosaurs did it," Varricchio said.
Crocodiles and birds assist their young by hatching them, feeding them, providing warmth and shelter, and protecting them from predators.
If these modern animals inherited such parental skills from their predecessors, the dinosaurs, it may help explain why dinosaur descendants have been so successful, Varricchio says.
The discovery "adds to the ever increasing picture of dinosaurs as being more sophisticated and more complex animals than what we imagined 50 years ago, when we had these sluggish, cold reptiles," Varricchio said.
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