The animals were found to have been grouped by age at the time of their deaths, with hatchlings and eggs in one area while skeletons of juveniles were clustered nearby. The eggs were arranged in layers within trenches. Adults were found alone or in pairs.
This phenomenon, llamado “age segregation,” signals a complex social structure, los investigadores dijeron, including adults that foraged for meals and cared for the young. The researchers suspect that members of the herd returned to the same spot during successive seasons to form breeding colonies.
“The young were staying with the adults at least until they reached adulthood. It could be that they stayed in the same herd after reaching adulthood, but we don’t have information to corroborate that hypothesis,” said paleontologist and study co-author Vincent Fernandez of the Natural History Museum in London.
Herd behavior also can protect young and vulnerable individuals from attack by predators.
“It’s a strategy for the survival of a species,” Fernandez said.
The oldest previous evidence for dinosaur herd behavior was from about 150 hace millones de años.
The nesting ground was situated on the dry margins of a lake featuring ferns and conifers in a warm but seasonal climate. The eggs are about the size of a chicken’s, and the skeleton of a hatchling fits in the palm of a human hand. The adults got as heavy as a hippo.
A scanning method called high-resolution X-ray computed tomography confirmed that the embryos inside the eggs indeed were of Mussaurus.
Mussaurus was a type of dinosaur called a sauropodomorph, which represented the first great success story among herbivorous dinosaurs. Sauropodomorphs were an evolutionary forerunner to a group called sauropods known for long necks and tails and four pillar-like legs.
The largest land animals in Earth’s history were the sauropod successors of sauropodomorphs, as exemplified by a later denizen of Patagonia called Argentinosaurus that reached perhaps 118 pies (36 metros) in length and upwards of 70 tons.