Was this small Triassic reptile the secret bipedal ancestor of all dinosaurs?

Nature · Published 3 October 2026 Swipe more like this →

In short: Euparkeria, a small carnivorous reptile from South Africa, has long captivated paleontologists. With its slender limbs and unique anatomy, researchers once suspected it was a facultative biped—a creature that could run on two legs. But modern biomechanical analysis suggests a different, more grounded reality for this ancient archosauriform.

Discovered in the Karoo Basin, Euparkeria lived approximately 247 million years ago during the Early to Middle Triassic. Named in honor of William Kitchen Parker, this reptile was a small carnivore with a boxy skull and rows of tiny, teardrop-shaped bony scutes along its back. For decades, its relationship to the archosaur lineage—which includes crocodiles, pterosaurs, and dinosaurs—made it a centerpiece in debates about the evolution of locomotion.

Early interpretations, including those by Rosalie Ewer in 1965, suggested Euparkeria could rear up on its hind legs to run. This theory relied on its hind limbs being slightly longer than its forelimbs and the presence of a calcaneal projection in the ankle, which seemed to offer the leverage needed for a semi-erect high walk. However, recent studies have dismantled this bipedal narrative. A 2023 analysis of weight distribution and muscle activation concluded that the animal was strictly quadrupedal. Its center of mass sat too far forward, and the energy required to maintain a bipedal stance would have caused its ankle muscles to fail.

Beyond its movement, Euparkeria offers a window into a harsh, seasonal environment. Scleral rings in its eye sockets suggest it was adapted to low-light conditions, likely navigating the long, dark winters of the high-latitude Karoo Basin. While it is no longer viewed as a direct ancestor to later archosaurs, it remains a vital link in understanding the stepwise evolution of the archosaurian body plan, sitting just outside the crown group that would eventually dominate the Mesozoic era.

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