Amargasaurus: Habitat, Behavior, and Diet

Name: Amargasaurus (Greek for "La Amarga lizard:); pronounced ah-MAR-gah-SORE-us

Habitat: Woodlands of South America

Historical Period: Early Cretaceous (130 million years ago)

Size and Weight: About 30 feet long and three tons

Diet: Plants

Distinguishing Characteristics: Relatively small size; prominent spines lining neck and back

About Amargasaurus

Most of the sauropods of the Mesozoic Era looked pretty much like most every other sauropod—long necks, squat trunks, long tails and elephant-like legs—but Amargasaurus was the exception that proved the rule. This relatively slim plant-eater ("only" about 30 feet long from head to tail and two to three tons) had a row of sharp spines lining its neck and back, the only sauropod known to have possessed such an imposing feature. (True, the later titanosaurs of the Cretaceous period, direct descendants of the sauropods, were covered with scutes and spiny knobs, but these were nowhere near as ornate as those on Amargasaurus.)

Why did the South American Amargasaurus evolve such prominent spines? As with similarly equipped dinosaurs (like the sailed Spinosaurus and Ouranosaurus), there are various possibilities: the spines may have helped to deter predators, they may have had some kind of role in temperature regulation (that is, if they were covered by a thin flap of skin capable of dissipating heat), or, most likely, they may simply have been a sexually selected characteristic (Amargasaurus males with more prominent spines being more attractive to females during mating season).

As distinctive as it was, Amargasaurus appears to have been closely related to two other unusual sauropods: Dicraeosaurus, which was also equipped with (much shorter) spines emanating from its neck and upper back, and Brachytrachelopan, which was distinguished by its unusually short neck, probably an evolutionary adaptation to the types of food available in its South American habitat. There are other examples of sauropods adapting fairly quickly to the resources of their ecosystems. Consider Europasaurus, a pint-sized plant eater that barely weighed a single ton since it was restricted to an island habitat.

Unfortunately, our knowledge of Amargasaurus is limited by the fact that only one fossil specimen of this dinosaur is known, discovered in Argentina in 1984 but only described in 1991 by the prominent South American paleontologist Jose F. Bonaparte. (Unusually, this specimen includes part of Amargasaurus' skull, a rarity since the skulls of sauropods are easily detached from the rest of their skeletons after death). Oddly enough, the same expedition responsible for the discovery of Amargasaurus also unearthed the type specimen of Carnotaurus, a short-armed, meat-eating dinosaur that lived about 50 million years later!