Add five new specimens to the worldwide collection of Tyrannosaurus rex skeletons. This summer, while working in remote areas in Montana, a large team led by paleontologist Jack Horner of the Museum of the Rockies in Bozeman, Montana, discovered five of these giant carnivores--a record number for a single field season. Although the fossils have not been completely excavated, preliminary studies suggest they are relatively complete; some, in fact, appear to retain 30% of their bones. One of them seems to be up to 10% larger than Sue, the biggest T. rex known, which is housed in the Field Museum in Chicago. What's more, "the preservation on some of them is exquisite," Horner says.
A fossil's scientific importance depends on how rare, complete, and well preserved it is. Over the past century, paleontologists have found bones from several hundred tyrannosaurs. Most of these, however, are fragments from skeletons that fell apart after death, and only a few dozen sport a substantial number of bones. Sue is hands down the winner, as she is beautifully preserved and about 90% complete.
Horner attributes the team's success to selecting relatively unstudied areas of Garfield County, Montana. "The idea was to go into areas that were difficult to get into and virtually impossible to get anything out of except by helicopter." He also had a lot of help. With funding from Universal Studios and Discovery Channel, as well as substantial backing from Microsoft mogul and amateur paleontologist Nathan Myhrvold, Horner was able to field a crew of about 50. Because they found so many fossils besides tyrannosaurs this season, the team couldn't complete the excavation and will return next year to retrieve them for further study.
Other experts are pleased by the news. "I'm glad to hear that a large number were found--and are bound for a museum. That's very critical," says Chris Brochu of the Field Museum in Chicago, who studies Sue. Finding more specimens that are relatively complete, he adds, could help reveal variation among individuals and perhaps settle the debate about whether T. rex was sexually dimorphic. The specimens may also provide clues into how the beast evolved and whether it was a scavenger or a predator.