Saltasaurus

• Name: Saltasaurus (Greek for "Salta lizard"); pronounced SALT-ah-SORE-us
• Habitat: Woodlands of South America
• Historical Period: Late Cretaceous (80 to 65 million years ago)
• Size and Weight: About 40 feet long and 10 tons
• Diet: Plants
• Distinguishing Characteristics: Relatively slim build; quadrupedal posture; short neck and legs; bony plates lining back

As titanosaurs go, the South American Saltasaurus was the runt of the litter; this dinosaur only weighed about 10 tons soaking wet, compared to 50 or 100 tons for more famous titanosaur cousins like Bruhathkayosaurus or Argentinosaurus. The petite size of Saltasaurus demands a convincing explanation, given that this dinosaur dates from the late Cretaceous period, about 70 million years ago; by this time, most titanosaurs had evolved to the super-heavyweight class. The most likely theory is that Saltasaurus was restricted to a remote South American ecosystem, lacking abundant vegetation, and "evolved down" so as not to exhaust the resources of its habit.

What set Saltasaurus and other titanosaurs apart from their sauropod ancestors was the bony armor lining their backs; in the case of Saltasaurus, this armor was so thick and knobby that paleontologists initially mistook this dinosaur (discovered in Argentina in 1975) for a specimen of Ankylosaurus. Clearly, newborn and juvenile titanosaurs attracted the notice of the numerous tyrannosaurs and raptors of the late Cretaceous period, and their backplates evolved as a nominal form of defense. (Not even the most overconfident Giganotosaurus would choose to target a full-grown titanosaur, which would have outweighed its antagonist three or four times over!)