Amargasaurus

Lore & Background

Amargasaurus was a relatively small sauropod, reaching about 9 to 10 meters in length and weighing roughly 2.5 to 3 tonnes. Its body followed the typical sauropod plan: a long tail and neck, a small head, and a barrel-shaped trunk supported by four column-like legs. The neck was shorter than in most other sauropods, a trait shared with its close relatives, and consisted of thirteen vertebrae that formed ball-and-socket joints. The trunk contained nine dorsal vertebrae and five fused sacral vertebrae, with robust ribs indicating a strong rib cage. Unlike many other sauropods, its dorsal vertebrae lacked deep lateral excavations known as pleurocoels. The most distinctive feature was the pair of extremely tall, upward-projecting neural spines on the neck and front of the back, which were bifurcated along their entire length, forming two parallel rows. These spines were circular in cross-section and tapered toward the tips; the tallest, on the eighth cervical vertebra, reached about 60 centimeters. They were bowed backward over the adjacent vertebrae. The last two dorsal vertebrae, the hip, and the foremost tail also had elongated spines, though these were not split but flared into paddle-shaped ends. The pelvic region was relatively wide, and the forelimbs were slightly shorter than the hind limbs. Only the rear part of the skull is preserved, but it likely had a broad, horselike snout with pencil-like teeth. The nostril opening was positioned in the posterior half of the skull, diagonally above a proportionally large eye opening. Uniquely among related dinosaurs, the skull had small parietal openings on its backside, which in other tetrapods are usually seen only in juveniles. The only known skeleton was discovered in 1984 in the La Amarga Formation of Argentina, which dates to the Early Cretaceous, about 130 to 120 million years ago. This herbivore shared its environment with at least three other sauropod genera, likely feeding at mid-height to reduce competition.

Reader's Guide

Amargasaurus is significant as one of the best-known sauropods from the Early Cretaceous of South America, providing valuable insights into the diversity and anatomy of the family Dicraeosauridae. Its most distinctive feature—the two parallel rows of tall, bifurcated neural spines on the neck and anterior dorsal vertebrae—has sparked debate about their function. Studies have suggested they may have supported a horn sheath or formed a scaffold for a neck sail, possibly used for display, combat, or defense. Amargasaurus also contributes to understanding sauropod feeding ecology; analysis of its inner ear and neck vertebrae suggests it habitually fed at mid-height, with its snout about 80 centimeters above the ground and a maximum feeding height of 2.7 meters. This likely helped reduce competition with other sauropod genera that shared its environment. The completeness of the skeleton, including a rare partial skull, makes Amargasaurus a key reference for dicraeosaurid anatomy and evolution.

Did You Know?

• Amargasaurus sported two parallel rows of tall spines down its neck and back, taller than in any other known sauropod.
• The name Amargasaurus alludes to the La Amarga Arroyo, with 'amarga' meaning 'bitter' in Spanish.
• The skeleton is currently stored in the collection of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires.