Lesothosaurus fossils provide new evidence for earliest social behaviour among bird-hipped dinosaurs

• Lesothosaurus diagnosticus is one of the earliest-known ornithischian, or bird-hipped, dinosaurs, living over 190 million years ago during the Early Jurassic period.
• Study of their fossils suggests that Lesothosaurus lived in herds which roamed southern Africa, providing some of the earliest evidence of social living in these dinosaurs.
• The discovery has been made following excavations of a ‘bonebed’ of fossils in South Africa, consisting of many skeletons jumbled and packed tightly together.

Excavations in South Africa, led by palaeontologists from the Evolutionary Studies Institute, Johannesburg, and the Natural History Museum, have unearthed a ‘bonebed’ of Lesothosaurus individuals, providing some of the earliest direct evidence of social living among ornithischian dinosaurs.

Previous research by Professor Paul Barrett, Merit Researcher at the Natural History Museum and co-author on the new paper, suggested that the dinosaur may have been a social animal. However, this was still uncertain. This new research, based on a greater number of individuals which were buried at the same time, provides far more conclusive evidence of social living within the species.

Living over 190 million years ago during the Early Jurassic, Lesothosaurus lived in what is now South Africa and Lesotho. It was a small, bipedal omnivore and one of the earliest ornithischian dinosaurs, the group that would later include iconic species like Triceratops and Stegosaurus.

It first appeared shortly after the beginning of the Jurassic Period, when the world was recovering from a time of intense volcanic activity which is believed to have been responsible for the end-Triassic mass extinction. This event paved the way for dinosaurs to become dominant for the next 135 million years.

In the Early Jurassic, however, many dinosaur groups had yet to reach enormous sizes, or develop a wide range of body shapes and structures. Lesothosaurus is often considered as a reference species for scientists trying to infer what the first ornithischian dinosaurs would have looked like.

Dr Jennifer Botha from the National Museum of South Africa, who led the study, was able to use these abundant fossils to show how Lesothosaurus grew up for the first time, by using high-powered microscopy to look inside the bones. Counting the growth lines present, rather like tree rings, allowed her to infer that Lesothosaurus reached adult size in only 2–4 years.

Professor Paul Barrett, Merit Researcher at the Natural History Museum and co-author on the paper, said:

'Until now, we didn't have direct evidence that Lesothosaurus lived together in groups.

'We know that later ornithischians had conspicuous features, such as the horns and frills of Triceratops, which were used for communication and other social behaviours, but Lesothosaurus lacks these obvious bony characteristics. This shows Lesothosaurus were already developing aspects of its social biology before these structures evolved.

'Living in a herd offers these dinosaurs the same benefits we'd expect from herd living today. Herds provide protection against predation by reducing the chance of any individual being attacked, as well as by appearing more intimidating to a predator.'

The study “Osteohistology and taphonomy support social aggregation in the early ornithischian dinosaur Lesothosaurus diagnosticus is published in Paleaontology. It can be accessed here after publication.

Notes to editors

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Images and paper available to download here.

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