Amargasaurus

Lore & Background

The skeleton was discovered in 1984 in sedimentary rocks of the La Amarga Formation in northern Patagonia, about 70 kilometers south of Zapala. It is reasonably complete, including a partial skull, and is stored in the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires. Amargasaurus was a relatively small sauropod, reaching a length of around 9 to 10 meters and weighing roughly 2.5 to 3 tonnes. It had a typical sauropod body plan: a long tail and neck, a small head, and a barrel-shaped trunk supported by four column-like legs. Its neck was shorter than in most other sauropods, consisting of thirteen vertebrae, and measured about 136% of the length of its dorsal vertebral column. The most distinctive feature was two parallel rows of extremely tall, upward-projecting neural spines running down the neck and back, taller than in any other known sauropod. These spines were bifurcated along their entire length, circular in cross-section, and tapered toward their tips; the tallest, on the eighth cervical vertebra, reached about 60 centimeters. They were bowed backward on the neck. The last two dorsal vertebrae, the hip, and the foremost tail also had elongated spines, but these were not bifurcated and flared into paddle-shaped ends. The skull is only partially preserved, but it likely had a broad, horse-like snout with pencil-like teeth. The nostril opening was positioned in the posterior half of the skull, diagonally above a proportionally large eye opening. Unusually, small parietal openings (fontanelles) were present on the back of the skull, a feature typically seen only in juvenile tetrapods. The forelimbs were somewhat shorter than the hind limbs, and the pelvic region was relatively wide.

Reader's Guide

Amargasaurus is significant as one of the best-known sauropods from the Early Cretaceous, providing valuable insight into the diversity of sauropod body plans. Its most distinctive feature—the two parallel rows of tall, bifurcated neural spines on the neck and back—has prompted several studies on their function. Hypotheses include that the spines supported a horn sheath, were connected by ligaments forming a neck sail, or were used for display, combat, or defense. As a member of the Dicraeosauridae, Amargasaurus had a shorter neck and smaller body size than many other sauropods, and it likely fed at mid-height, with a habitual snout position about 80 centimeters above the ground. The skeleton's completeness, including a rare sauropod skull, makes it a key reference for understanding dicraeosaurid anatomy and evolution.

Did You Know?

• Amargasaurus was small for a sauropod, measuring 9 to 13 meters in length and weighing about 2.5–4 metric tons.
• The tallest spines on its neck reached 60 centimeters on the 8th cervical vertebra.
• The species name Amargasaurus cazaui honors geologist Luis Cazau, who informed the team about the La Amarga Formation.