Huayracursor jaguensis Fossil Challenges Prevailing Theories on the Evolution of Sauropod Neck Lengths

Deep in Argentina’s Andes Mountains, paleontologists have uncovered the remains of a small dinosaur, giving insight into the early adaptations that characterized sauropod dinosaurs, specifically the extended neck seen in diplodocus.

The fossil, named Huayracursor jaguensis, represents a partial skeleton of a creature that roamed the Earth during the Triassic period, roughly 230 million years ago. It is estimated to have measured around 2 meters in length and weighed about 18 kilograms.

Subsequent sauropods like brontosaurus and Patagotitan would grow to impressive sizes—over 35 meters long and weighing more than 70 tons, marking them as the largest and longest-necked animals in history.

Previously, scientists believed that the ancestors of these long-necked, herbivorous dinosaurs were small, short-necked, and possibly even omnivorous.

At the same time, other smaller sauropods, such as homo jaguensis, measured approximately 1 meter and displayed no signs of elongated neck bones, unlike the newly identified species. This led paleontologists to think that substantial growth in size and neck elongation in sauropods didn’t occur until millions of years later.

The discovery of homo jaguensis at Santo Domingo Creek in northwestern Argentina has prompted a reevaluation of how these dinosaurs developed their iconic long necks, according to Martin Hechenleitner from Argentina’s National Council for Scientific and Technical Research.

“Waila cursor presents a different narrative than the gradual transition model,” Hechenleitner points out. “This is evident since it coexisted with closely related species that were smaller and had relatively shorter necks.”

This dinosaur had a small skull, muscular hind limbs, slender hips, and notably short arms, with relatively large and robust hands compared to other dinosaurs of its era.

This suggests that the traits of increased size and neck elongation emerged early in this evolutionary line, Hechenleitner explains.

“Waila cursor allows us to trace the origins of elongated necks and larger body sizes back to the dawn of dinosaurs in the fossil record,” he says, referencing species like argentinosaurus and Patagotitan, which emerged from a lineage that originated over 100 million years ago, with early bipedal forms measuring just over a meter long and weighing between 10 and 15 kilograms.

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