By Will Dunham
(Reuters) - The world's biggest T. rex is getting ready for a cutting-edge makeover.
The Field Museum in Chicago said on Wednesday it will take down and remount the 40-1/2-foot-long (12.3-meter) Tyrannosaurus nicknamed Sue, perhaps the world's most famous dinosaur fossil, in a way that embodies the latest understanding of this ferocious Cretaceous Period predator.
The big T. rex will move to a new exhibition space in the museum, while a cast of the skeleton of the largest-known dinosaur, Patagotitan mayorum, will take the spot Sue now occupies in the museum's Stanley Field Hall.
Patagotitan, a long-necked, four-legged plant-eater that was 122 feet (37.2 meters) long and weighed 70 tons, lived in Argentina 100 million years ago, more than 30 million years before T. rex stalked western North America. The biggest land animal on record, it was a member of a dinosaur group called titanosaurs.
The museum next spring will unveil the fiberglass Patagotitan skeleton, which is being cast from fossils of seven Patagotitan individuals, and for two years will display some of the genuine fossils, including an 8-foot (2.4 meter) thighbone.
Named for the woman who discovered the fossils in South Dakota in 1990, Sue is the largest, most complete and best-preserved Tyrannosaurus rex ever unearthed. The museum bought the fossils at auction for $8.4 million.
Sue will be taken down in February and put up again with noteworthy changes in anatomy and stance in its new exhibition hall in spring 2019, museum scientists said.
"We are making several adjustments to the skeleton to reflect new and improved knowledge," said paleontologist Pete Makovicky, the museum's associate curator of dinosaurs.
The most striking change, Makovicky said, will be the addition of gastralia, bones resembling an additional set of ribs spanning the belly that may have provided structural support to help the dinosaur breathe. Adding these bones will illustrate just how massive Sue was and that it boasted a bulging belly, he added.
The scientists concluded that the bone mounted as Sue's wishbone was misidentified in 2000 and they will replace it with the dinosaur's actual wishbone, or furcula, the fused collar bones typical of meat-eating dinosaurs and their evolutionary descendants the birds.
They also will adjust the ribs to produce a slimmer, less barrel-shaped chest, and arrange the right leg so Sue is not crouching as much.
"Often when you do something as expensive as mounting a vertebrate fossil skeleton for display you only get one shot at it. I'm happy we're going to fix and update this incredible fossil," said paleontologist Bill Simpson, who heads the museum's geological collections.
LIFESPAN AND BITE FORCE
Makovicky noted the accumulation of knowledge about T. rex and its cousins since 2000.
"We now know more about tyrannosaur lifespans -- around 30 years; how they grew -- very fast as teenagers; and using computer models of Sue we revised their body mass upward to 9 or more tons, from 5 to 7 tons," Makovicky said.
Ongoing research is examining the molecular composition of cartilage preserved in T. rex bones, and recent studies have shown it possessed the most powerful bite of any land animal ever, Makovicky added.
When the Patagotitan skeleton is mounted, visitors will be able to walk underneath it and touch it. Its head will reach the museum's second-floor balcony nearly 30 feet (9 meters) up. Another Patagotitan skeleton is displayed at the American Museum of Natural History in New York.
The museum said a $16.5 million gift from the Kenneth C. Griffin Charitable Fund, established by the founder and chief executive of hedge fund firm Citadel LLC, enabled it to carry out Sue's makeover and add the Patagotitan. The changes coincide with the museum's 125th anniversary in 2018.
(Reporting by Will Dunham; Editing by Sandra Maler)