A newly discovered 230-million-year-old dinosaur fossil from Argentina suggests that the evolution of long necks in sauropods began much earlier than previously thought. Named Huayracursor jaguensis, the specimen shows early signs of neck elongation in a small, bipedal dinosaur. This finding challenges the idea of a gradual transition in sauropodomorph evolution.
Palaeontologists have unearthed a partial skeleton of Huayracursor jaguensis in the Argentinian Andes, specifically at Santo Domingo Creek in north-west Argentina. Dated to the Triassic period around 230 million years ago, this dinosaur measured about 2 metres in length and weighed approximately 18 kilograms.
The fossil, discovered by Martín Hechenleitner of Argentina’s National Scientific and Technical Research Council and his colleagues, features a small skull, robust hind limbs, slender hips, and short arms with large, robust hands. Unlike its contemporaries, which were around a metre long with proportionally shorter necks, H. jaguensis exhibits the first hints of extended neck bones.
Until this discovery, scientists believed that early sauropodomorphs—precursors to giant long-necked herbivores like Brontosaurus and Patagotitan—were small, short-necked, and possibly omnivorous. These later sauropods grew to over 35 metres long and more than 70 tonnes. However, H. jaguensis coexisted with smaller relatives, indicating that body size increases and neck lengthening occurred from the outset of dinosaur evolution.
“Huayracursor breaks somewhat with this idea of a gradual transition, because it coexisted with its small, proportionally shorter-necked relatives,” says Hechenleitner. He adds, “Huayracursor drags the origin of the long neck and larger body size towards the first appearance of dinosaurs in the fossil record.”
“It’s fascinating to think that giant animals up to 40 meters long and over 30 tonnes, like Argentinosaurus and Patagotitan, are part of a lineage that began more than 100 million years earlier, with bipedal forms just over a metre long and a mere 10 to 15 kilograms [in weight],” Hechenleitner notes.
The research is published in Nature (DOI: 10.1038/s41586-025-09634-3), reshaping our understanding of how sauropods developed their iconic features.