When most people picture a sauropod, they imagine a colossal, four-legged creature with a neck that reaches the treetops from a standing position on all fours. But a new study published in Palaeontology reveals that two South American sauropod species had a hidden talent: they could rise up on their hind legs and stand tall like giants, especially when they were young.
About 66 million years ago, during the Late Cretaceous period, two sauropods — Uberabatitan ribeiroi from Brazil and Neuquensaurus australis from Argentina — evolved a bone structure that allowed them to shift onto their hind legs. While elephant-sized as adults, they were modest compared to the largest sauropods like Argentinosaurus. Adult Uberabatitan could reach 26 meters in length, making them the largest dinosaurs known from Brazil.
Using finite element analysis (FEA), a standard engineering technique for testing stress on bridges and buildings, researchers created digital reconstructions of femurs from seven sauropod species. They simulated the forces that gravity and body weight would place on the thigh bone when the animal stood upright.
Standing on two legs gave these dinosaurs several advantages. It allowed them to reach leaves high in trees that were inaccessible from a four-legged stance. The upright posture may also have made them appear larger and more intimidating to predators. Researchers also suggest it could have played a role in courtship displays or mating.
The study, led by Julian Silva Júnior of São Paulo State University in collaboration with the University of Tübingen in Germany, is the first to use finite element analysis specifically to test bipedal posture in sauropods. "Smaller sauropods like these had a bone and muscle structure that allowed them to stand more easily and for longer on their two hind legs," Silva Júnior explained. "Larger ones were probably also able to stand, but for a shorter time and with less comfort."
The finding adds a new dimension to how scientists understand sauropod behavior and ecology. For decades, sauropods were assumed to be strict quadrupeds that rarely lifted their front legs off the ground. The discovery that at least two species regularly used a bipedal posture — and that this ability diminished with age — suggests that dinosaur behavior was more complex and varied across life stages than previously appreciated. It also shows how engineering tools designed for modern infrastructure can unlock secrets from fossils that have been buried for 66 million years.