The king of the dinosaurs is back on display at the Carnegie Museum of Natural History -- and this time, it has an enemy.

The new exhibit, which opens Sunday, Father's Day, marking the final phase of a three-year, $36 million expansion and upgrade of the museum's Dinosaur Hall, features two Tyrannosaurus rexes on the verge of battle.

"It's not common to see two T. rexes next to each other, let alone one being an original," said Matt Lamanna, assistant curator of vertebrate paleontology at the Carnegie Museum of Natural History and lead scientific adviser for the exhibit.

One of the T. rexes is the original holotype that was found in Hell Creek, Mont., in 1902. A holotype is the first specimen of a species that is discovered and is used to define the species. The newer T. rex, nicknamed Peck's Rex, was discovered in Fort Peck, Mont., in 1997.

The museum purchased the original T. rex from the American Museum of Natural History in 1941 for $7,000 -- equivalent to about $100,000 today.

"It was the steal of the century," said Ellen James, manager of public relations and communications at the Carnegie Museum of Natural History. "The last time a T. rex skeleton was sold, it was for $8.3 million."

The holotype was put on display the year after it was purchased, but there were mistakes.

For one, the skull was inaccurately reconstructed because only eight out of the dozens of skull and lower jaw bones had been recovered. When the holotype was dismantled in 2005 for reconstruction, the museum collected casts from a similar T. rex in Bozeman, Mont., to form a new skull.

Posture was another mistake. When the dinosaur was first discovered, paleontologists believed that it stood upright. However, discoveries in the 1960s showed that the T. rex stood nearly horizontal, with its tail elevated and curved.

The appropriate changes to the dinosaur could not be made at the time because of a lack of funds. But the T. rexes in the new exhibit -- part of the new "Dinosaurs in Their Time'' exhibition that converted a former outdoor atrium into enclosed space for the new hall, tripling the exhibition space and creating room for 19 dinosaurs, nearly double the previous 10 -- will illustrate proper posture.

"We probably have the most modern T. rex display in the world. It is up to date with current understanding," Lamanna said.

The exhibit displays the two T. rexes face to face with the holotype protecting the carcass of an Edmontosaurus regalis from the Peck's Rex, which is looking to steal the meal.

"One T. rex has either killed or found the carcass, and it's eating it when the other finds it and tries to get a free meal. Then it's left to the visitor to guess what happens next. Do they fight one another? Or does the other dinosaur walk away with his tail in between his legs?" Lamanna said.

Three other dinosaurs are also in the scene: Corythosaurus casuarius, Pachycephalosaurus wyomingensis and Triceratops prorsus. These dinosaurs surround the two T. rexes and act as spectators to the possible fight.

"The other dinosaurs ... all look nervous and edgy because that's what they would've felt if they were witnessing the two huge T. rexes," Lamanna said.

The new exhibit is also an environmental re-creation of landscape. Paleontologists were able to re-create different plants and trees from the Late Cretaceous Period from fossils found in the Hell Creek formation.

"It's like a snapshot in time," he said. "It will open people's eyes to the fact that a lot of today's world evolved from the age of dinosaurs. Every plant and animal here is from Hell Creek."

Plants included in the exhibit are descendants of poppies, buttercups, sycamore, magnolia and palm trees.

The museum hopes that this scenic re-creation will serve as a visual supplement, not substitute, for the educational information available at the exhibit. "We realize that people will come here for the visual. The visual is great, but I don't know of another educationally rich exhibit in the world," Lamanna said.

Museum admission: Adults, $15; seniors, $12; children, $11. Members and children under 3 don't pay a fee.