Findings from new research on a vast fossil site in Patagonia suggest that some of the earliest dinosaurs lived in herds and that this behaviour may have been central to the dinosaurs’ success.

A significant part of the findings was based on the discovery of embryos of the same species inside fossilized eggs. These findings were reported in the journal Scientific Reports.

Studies have shown that some dinosaurs lived in herds during the Cretaceous Period (the latest stage of the dinosaur Era). Nevertheless, there remains a major question regarding when and how this behaviour first appeared in their evolutionary history.

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Scientists discovered a 190-million-year-old dinosaur nesting ground in the early 2000s, which also contained juvenile skeletons belonging to Mussaurus patagonicus, a primitive, herbivorous sauropodomorph dinosaur (forerunner of the large, long-necked dinosaurs) in Patagonia (Argentina). 

“Such a preserved site was bound to provide us with a lot of information about how early dinosaurs lived,” explained Diego Pol, the palaeontologist at CONICET who discovered the site.

The eggs found on the site could shed light on how early dinosaurs lived.

“It is hard to find fossil eggs, and even more to find fossil eggs with embryos inside, as you need very special conditions for their fossilization,” explains Pol.

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High-resolution computed tomography revealed fossilized embryos of Mussaurus within some of the eggs, indicating that all these fossils originated from a communal breeding site of a single dinosaur species.

Researchers also studied the site itself. Numerous fossils were found in various rock horizons within the same locality, indicating that Mussaurus returned to form breeding colonies during successive seasons.

Among the main characteristics of this fossil site is the fact that dinosaur skeletons were not randomly spread around the site, but instead were grouped by age.

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Fossils of dinosaur babies were found near the nests. While, one-year-old Mussaurus youngsters were found close to each other, including a cluster of eleven skeletons in resting positions, indicating that the species formed schools of young individuals. Adults and subadults were found together in pairs or alone, but all within one square kilometre.

A well-organized herd structure also appears to have been observed, making this the first evidence of such complex social behaviour in an early dinosaur. This finding predates other fossil records of dinosaurs with evolved social behaviour by more than 40 million years. 

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The scientists compared these results with other fossil egg sites from South Africa and China and concluded that social behaviour can be traced back to dinosaur origins.

“These are not the oldest dinosaurs, but they are the oldest dinosaurs for which a herd behaviour has been proposed. Mussaurus belongs to the first successful family of herbivorous dinosaurs, so we postulate that being social and protecting their young together as a herd may have been part of the reason these long-necked dinosaurs were so common in all continents”, concludes Pol.

(With inputs from agencies)