Description and Classification

Amargasaurus was a four-legged, plant-eating dinosaur, but it was relatively small for a sauropod. It measured around 9 to 10 meters (30 to 33 feet) in length and likely weighed about 2.6 metric tons (2.9 short tons). Like other sauropods such as Brachiosaurus or Apatosaurus, it had a long neck and a long tail, although its neck was proportionally shorter and more robust compared to many of its giant relatives. Its most remarkable feature was the double row of very tall, pointed spines that extended from the vertebrae of its neck and back. These spines were longest on the neck—up to 60 centimeters (2 feet) high—and gradually became shorter towards the hips.

Amargasaurus belongs to the group Sauropoda, which includes the largest land animals ever to have lived. Specifically, it is classified within the family Dicraeosauridae. Dinosaurs in this family, such as Dicraeosaurus from Africa and Bajadasaurus from Argentina, are known for having elongated or forked neural spines on their vertebrae. Amargasaurus is the type species of its genus. It is considered a close relative to other dicraeosaurids like the aforementioned Dicraeosaurus and Bajadasaurus, as well as the very short-necked Brachytrachelopan.

Distinguishing Features

Several unique features help scientists identify Amargasaurus and differentiate it from other dinosaurs:

• Two parallel rows of very tall, pointed neural spines running along its neck and back. These spines were much taller and more prominent than those on its close relative Dicraeosaurus.
• A relatively short and thick neck for a sauropod, which would have limited its feeding height compared to other long-necked sauropods.
• The neural spines on its neck vertebrae were deeply forked, forming the distinctive double row. The spines on its back were single and blade-like.
• A smaller overall body size when compared to many other sauropod dinosaurs from the Cretaceous period.

Paleoenvironment and Diet

Amargasaurus lived during the Early Cretaceous period. Its fossilized skeleton was discovered in the La Amarga Formation in the Neuquén Basin of Argentina. During that time, this region was a floodplain landscape characterized by braided river systems, shallow lakes, and ponds. The climate was likely warm and semi-arid, with distinct wet and dry seasons. Amargasaurus shared this environment with other dinosaurs, including small predatory theropods like the abelisaurid Ligabueino, and other herbivorous dinosaurs such as the unusual armored sauropod Agustinia and various iguanodontians.

As an herbivore, Amargasaurus fed on plants. Its shorter neck and the anatomy of its skull and teeth suggest it was probably a low to medium-height browser, feeding on vegetation like ferns, cycads, and conifers that grew up to about 2.7 meters (9 feet) off the ground. It had simple, peg-like teeth, which were suitable for stripping leaves and young shoots off branches but not for extensive chewing. Like other sauropods, it likely swallowed its food in large mouthfuls, relying on its complex digestive system, possibly containing gastroliths (stomach stones), to break down the tough plant material.

Significance and Ongoing Research

Amargasaurus is an important dinosaur because it provides valuable insights into the diversity and evolutionary adaptations of sauropods, particularly within the Dicraeosauridae family. Its highly distinctive double row of spines makes it one of the most recognizable sauropods and has sparked considerable scientific discussion about the appearance and behavior of these animals. Studying Amargasaurus helps paleontologists better understand the ecosystems of Early Cretaceous South America and the unique evolutionary paths taken by its dinosaurian inhabitants.

The exact function of Amargasaurus’s tall neck and back spines remains a primary subject of ongoing research and debate. Scientists have proposed several hypotheses: the spines might have been used for visual display, either to attract mates, intimidate rivals, or for species recognition. Another idea is that they supported a skin sail or sails, which could have been used for display or possibly to help regulate body temperature. Alternatively, the spines might have been covered in a hard sheath of keratin (the same material as fingernails and horns) and could have offered some protection, although their structure suggests they might have been too delicate for direct use in combat. It is also possible they supported a fatty hump for energy storage. Further research, including biomechanical studies and comparisons with modern animals, continues to explore these possibilities, aiming to shed more light on the life and appearance of this fascinating dinosaur.