Dinosaurs: Herding behaviour began much earlier than we thought

By Chen Ly

Dinosaurs were living together in herds earlier than we realised, suggests an analysis of the fossils of sauropodomorphs – a group that includes large herbivores with long necks and small heads, like Diplodocus.

Sauropodomorphs were among the first dinosaurs to appear on Earth. They were the dominant land-dwelling herbivores for 40 million years, during the Late Triassic and Early Jurassic periods. There are many proposed reasons for the successful survival of these dinosaurs, such as their height, large size and rapid rates of growth.

Diego Pol at the Museum of Palaeontology Egidio Feruglio in Trelew, Argentina, and his colleagues think that their social behaviour may have also played a key role in this success.

In approximately 193-million-year-old rocks found in the Laguna Colorada Formation in Argentina, the team discovered the fossilised remains of 69 individuals belonging to a bipedal species of early sauropodomorph called Mussaurus patagonicus and more than 100 eggs. Previous excavations at the site had uncovered the remains of an additional 11 individuals.

The researchers discovered that each nest contained between eight and 30 eggs, and the close spacing of the nests suggests that the area was a common breeding grounds for the M. patagonicus.

Nearby, they found the remains of eight hatchlings clustered together, a mere 50 metres away from a  group of 11 juvenile M. patagonicus that were all less than a year old. They also found nine individuals that were older than juveniles but younger than adults and were close together, as well as a pair of adults together.

All of this evidence suggests that M. patagonicus lived in herds. Prior to this, the earliest evidence of dinosaur herding behaviour was from rocks that are roughly 150 million years old. The new findings extend that record by 40 million years.

The discovery of both young and old M. patagonicus in such close proximity indicates that they lived in herds throughout their lives, and mainly interacted with those their own age. “This is fairly complex social behaviour and social interaction – we had no idea early dinosaurs were so social,” says Pol.

For these dinosaurs, living together in social cohesion would have been a very efficient way to protect their young from dangers such as predators, he says. The study’s authors suggest that this social behaviour influenced sauropodomorphs’ early success as terrestrial herbivores.

Journal reference: Scientific Reports, DOI: 10.1038/s41598-021-99176-1

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