Completing a titan by getting a head.

When paleontologists unearthed the skeleton of a 70-million-year-old titanosaur in Madagascar in the late 1990s, they also recovered something that had been missing from previous such finds: a skull that matches the body.

Titanosaurs form one group of sauropod dinosaurs, the massive, four-legged plant eaters that had long necks and tails. Most types died out more than 100 million years ago, but titanosaurs were more successful. They stuck around until the extinction of all dinosaurs about 65 million years ago, and their fossils have been found on every continent except Antarctica.

Scientists have described almost three dozen types of titanosaurs, says Kristina Curry Rogers, a vertebrate paleontologist at the Science Museum of Minnesota in St. Paul. Until recently, researchers knew most of these species only from skeletal fragments and isolated bits of skull.

In contrast, the emerging portrait of the new Madagascan titanosaur is based on the skeleton of a juvenile that's about 75 percent complete, as well as skull portions of two juveniles found with it. These bone fragments are consistent with the nearly complete skull of an adult that Curry Rogers and her team excavated from nearby rocks of the same age. Adults of the new species--which the team dubbed Rapetosaurus krausei in the Aug. 2 NATURE--would have been about 12 meters long.

The image of what a complete titanosaur looked like may help scientists solve broader paleontological puzzles, Curry Rogers notes. Researchers know two Mongolian titanosaurs only from their skulls, and most South American species left fossils with no heads. A better theory about the relationship among all the dinosaurs in this group could illuminate how they evolved and dispersed around the globe.