When paleontologists mount dinosaur bones they try to capture what the dinosaurs would have looked like when they were alive. That's why almost all dinosaurs are mounted in dynamic poses: walking, running, attaching or defending.

Dr. Sereno's sketch of an adult Jobaria posed in a hind-limb stand. The human silhouette establishes scale.

When Sereno's team prepared the bones of the juvenile Jobaria, a surprising discovery came to light: something had bitten the juvenile and left tooth marks on its ribs!

Afrovenator was the dominant predator in the region at that time and its teeth were found at the theropod site. Dr. Sereno concluded it was likely the bite marks were made by Afrovenator, the "African Hunter," that had attacked the juvenile.

Based on this fascinating discovery, Dr. Sereno decided to mount a juvenile skeleton of Jobaria alongside an adult skeleton warding off an attack by Afrovenator.

Not that long ago, paleontologists would have rejected the notion that a 20-ton sauropod like Jobaria could rear up on its hind legs.

Paleontologists argued that these giant animals - the largest sauropod probably weighed about 80 tons—lived their whole lives in the water, where they could wade around with less effort. Paleontologists couldn't believe that such big and heavy animals could support their own weight.

Today we know that sauropods could support their weight and did walk on land. While it's true that sauropods are very heavy, their bones are also much more robust than similar bones in today's large living animals such as elephants. Furthermore, sauropod skeletons like Jobaria are found in land, not water, deposits. But the most convincing evidence comes from sauropod trackways: these preserved footprints show that sauropods must have walked on land.

But could 20-ton Jobaria stand on its hind legs, supporting all that weight on just two legs? To answer that question Dr. Sereno turned to today's largest living four-footed animal, the African elephant.