This is a cast of juvenile Tyrannosaurus rex jaws/teeth found in Montana in 1966. Studies have shown that it was less than 3 years old when it died. The skull shape differs from a mature animal and was once thought to be a different species. These fossils were on display at the Carnegie Museum for Natural History in 2011.
Here is the mature skull shown in an exhibit at the museum. Discovered at Hell Creek, Montana and given the accession number CM 9380. This carnivore prowled the plains of the western United States and southwestern Canada in the Late Cretaceous Period (68-66 million years ago), Mesozoic Era.
This skull contains the actual fossils that are part of the holotype for the T. rex. The holotype was discovered by Barnum Brown in 1902. Those remains were used to create a intact skeleton for the American Museum of Natural History in New York city. The Carnegie Museum acquired this skeleton in 1941. In 2003, the museum dismantled the skeleton for analysis and cleaning. The work was finished in 2008 and the dinosaur was presented in its new pose. Read about the process at the PaleoLab section of their web site: http://www.carnegiemnh.org/exhibitions/paleolab/rex.html
See this site at the museum web site for media images of the skull including shots from inside the skull: http://www.carnegiemnh.org/press/08-apr-jun/051208rex-images.htm