Enigmacursor Mollyborthwickae: Labrador-Sized Dinosaur That Swiftly Ran Along Rivers 150 Million Years Ago in the US!

In a thrilling 2025 revelation, scientists have unveiled Enigmacursor mollyborthwickae—a nimble, dog-sized neornithischian dinosaur that darted across Late Jurᴀssic floodplains of Colorado, USA, some 145–150 million years ago. Roughly the size of a Labrador retriever (about 1.8 meters long and 64 cm tall at the hips), this speedy herbivore earned its name—“mysterious runner”—for its exceptional agility and long legs.

The most complete three-dimensionally preserved small ornithischian from the iconic Morrison Formation, the specimen was acquired thanks to a generous donation by Molly Borthwick and is now permanently displayed at London’s Natural History Museum in Earth Hall. Described June 25, 2025, in Royal Society Open Science, the partial skeleton reveals dense hips and elongated limbs optimized for rapid escape from predators like Allosaurus, allowing it to thrive in the shadows of giants such as Diplodocus and Stegosaurus.

This discovery dramatically boosts our understanding of Morrison Formation diversity. Previously, small ornithischians were poorly known; Enigmacursor proves they were far more varied and successful than thought. Its bipedal build and runner adaptations highlight an early experiment in lightweight, fast-moving plant-eaters that coexisted with mᴀssive sauropods and armored stegosaurs on ancient river plains.

Paleontologists hail it as a “puzzle solver” for Jurᴀssic ecosystems. As one expert noted, its long legs kept it “one step ahead of danger.” From the Morrison badlands, Enigmacursor mollyborthwickae emerges as a charming missing link—proof that even tiny dinosaurs left big footprints in evolutionary history.