The discovery of a new species of long-necked dinosaur in Patagonia, Argentina, introduced the world to Bajadasaurus, a sauropod instantly recognizable by the paired spikes projecting from its neck. This reptile, formally described in 2019, represents a distinct branch on the sauropod family tree, challenging previous ideas about the evolution and function of vertebral spines in these giant herbivores. The bizarre, forward-curving arrangement of its neck structures sets it apart from its relatives.
Placement Among Sauropods
Bajadasaurus is classified as a member of the Dicraeosauridae family, a group within the larger Sauropoda that includes relatively smaller, shorter-necked forms compared to giants like Brachiosaurus or Diplodocus. The full scientific name given to the species is Bajadasaurus pronuspinax, which translates roughly to the “Bajada lizard with bent-over-forward spines,” a direct reference to its most prominent anatomical feature and the location of its discovery. The fossil evidence places this animal firmly in the Early Cretaceous period, living approximately 145 to 132.9 million years ago.
The single known specimen was recovered from the Bajada Colorada Formation in Neuquén Province, located in northern Patagonia, Argentina. This specific geologic layer is known for preserving remains from the Late Berriasian to Valanginian stages of the Early Cretaceous. Within the Dicraeosauridae family, Bajadasaurus is closely related to the slightly later-living Amargasaurus, which inhabited the same general region of South America. Amargasaurus is also known for having elongated vertebral spines, but the morphology and orientation of the structures differ significantly between the two genera.
The Distinctive Neck and Back Spines
The defining feature of Bajadasaurus is the series of long, bifurcated, neural spines projecting from its cervical vertebrae. These bony extensions curve dramatically forward, an unusual posture that would have positioned the sharp tips over the animal’s head and neck. While other dicraeosaurids, such as Dicraeosaurus, had bifurcated spines, the length and pronounced forward angle of the Bajadasaurus structures are unique.
The neural spines of Bajadasaurus are distinct from those of Amargasaurus, whose equally long structures pointed generally backward over the body. Scientists hypothesize that the spines were not bare bone but were likely covered by a keratinous sheath, similar to the horns of modern mammals. This covering would have made the structures sharper and increased their visual impact.
The purpose of these striking spines remains a topic of scientific discussion, with several hypotheses proposed for their function. The most prominent theory is that they served as a form of passive defense against predators. The sharp, forward-pointing spines would have presented a dangerous, potentially lethal barrier to any large theropod attempting to attack the sauropod’s vulnerable neck or head.
Other possibilities suggest a role in visual communication, where the spines might have been used for species recognition, display during mating rituals, or establishing dominance within a herd. It has also been proposed that the spines could have supported a hump or sail-like structure made of soft tissue, which could have assisted in thermoregulation. However, the defensive function is often favored due to the robust nature and strategic, forward-facing orientation of the spines.
Environment and Behavior
The fossil evidence from the Bajada Colorada Formation suggests that Bajadasaurus lived in a dynamic, low-relief landscape dominated by a braided river system. This ancient environment consisted of sandstones, conglomerates, and siltstones, indicating a well-watered region likely supporting lush vegetation. This habitat would have provided ample resources for the herbivorous sauropod, which was a medium-sized species within its group, with estimates suggesting a length of around 40 feet.
Analysis of its skull and teeth indicates that Bajadasaurus was a low-browser, feeding on plants near the ground. Its slender skull held pencil-shaped teeth clustered at the front of the jaws, an adaptation suited for stripping foliage rather than grinding tough material. The anatomical structure of the neck and head orientation further supports this low-feeding behavior, as the eye sockets were positioned to allow the animal to look forward even while its head was angled downward.
The ecosystem it inhabited was diverse, with Bajadasaurus sharing its home with other sauropods, including the diplodocid Leinkupal and the early titanosaur Ninjatitan. The presence of various theropods, which included both large abelisaurids and other meat-eating dinosaurs, highlights the need for the defensive structures seen on the sauropod’s neck. The unique features of Bajadasaurus allowed it to occupy a specific ecological niche, minimizing competition with the other plant-eaters while maximizing protection from the region’s predators.