Fossilized remains of sauropodomorphs – large, long-necked herbivores that lived during the MesozoicThe Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles and the Age of Conifers and is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous.”>Mesozoic Era – may provide the earliest evidence of herd living in dinosaurs, according to a study published in Scientific Reports.
Diego Pol and colleagues discovered the fossilized skeletal remains of 69 individuals and 100 eggs belonging to the species Mussaurus patagonicus in the Laguna Colorada Formation in Patagonia, Argentina. The authors found that most of the eggs were arranged into clusters of between eight and 30 eggs. X-ray imaging of five of these clusters revealed that eggs contained embryos of Mussaurus patagonicus and were arranged in two to three layers within trenches, suggesting that they were contained within nests within a common breeding ground.
The authors analyzed the size and type of bone tissue of the skeletal remains to determine the ages of the fossilized individuals. They identified a cluster of 11 juveniles aged less than a year old, two adults that were found together, and nine individuals that were older than juveniles but younger than adults. The authors suggest that the presence of age-specific clusters of individuals in the same location could indicate that M. patagonicus lived in herds throughout their lives but primarily associated with others their own age within herds. Analysis of the rocks surrounding the remains suggests that the remains are approximately 193 million years old, pre-dating previous records of complex social behavior among dinosaurs by over 40 million years.
The authors speculate that the evolution of complex social behavior among sauropodomorphs may have coincided with increases in body size that occurred between 227 and 208 million years ago. Meeting the increased energy requirements associated with larger body sizes may have required M. patagonicus to coordinate their behaviors and form herds in order to forage over large distances, they suggest.
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Reference: “Earliest evidence of herd-living and age segregation amongst dinosaurs” by Diego Pol, Adriana C. Mancuso, Roger M. H. Smith, Claudia A. Marsicano, Jahandar Ramezani, Ignacio A. Cerda, Alejandro Otero and Vincent Fernandez, 21 October 2021, Scientific Reports.