Was the dawn plunderer a fearsome predator or a humble plant-eater?

Nature · Published 3 October 2026 Swipe more like this →

In short: Discovered in Argentina's Valley of the Moon, Eoraptor is one of the earliest dinosaurs ever found. This small, swift biped lived 231 million years ago, but its true identity remains a puzzle. Scientists have debated for decades whether this creature was a primitive meat-eater or an early ancestor of giants.

Named in 1993 by Paul Sereno and his team, Eoraptor lunensis—the 'dawn plunderer from the Valley of the Moon'—represents a critical window into dinosaur evolution. Unearthed in the Ischigualasto Formation of northwestern Argentina, the holotype specimen PVSJ 512 was found in muddy siltstone deposited during the Carnian stage of the Triassic period, roughly 235 to 228 million years ago. This small dinosaur, measuring about 1.2 to 1.3 meters in length and weighing under 10 kilograms, was a fast, digitigrade runner with hollow-shafted long bones.

The classification of Eoraptor has been notoriously unstable. Initially described as a basal theropod due to its grasping, functionally tridactyl hand, subsequent research has frequently shifted its position. By 2011, some studies placed it firmly as a theropod, while others, including a 2013 redescription by Sereno, categorized it as a basal sauropodomorph. More recent analyses, such as the 2025 study on Huayracursor, continue to recover it as an early-diverging member of the Sauropodomorpha. This taxonomic tug-of-war highlights the difficulty of placing a creature that lacks the specialized features of later, more distinct dinosaur groups.

Eoraptor’s diet is equally complex. Its heterodont dentition—featuring both serrated, recurved teeth in the upper jaw and leaf-shaped teeth in the lower jaw—suggests an omnivorous lifestyle. Unlike later theropods, it lacked a sliding jaw joint for handling large prey, yet it possessed large claws on its three longest digits. Living in a volcanically active, humid floodplain, Eoraptor was far from dominant; dinosaur fossils make up only about 6% of the total samples recovered from its environment, where non-dinosaurian tetrapods were significantly more abundant. Whether it was a young adult or a juvenile remains a point of nuance, with researchers noting a mix of mature and immature skeletal traits.

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