A partial Tyrannosaurus rex skeleton discovered on Wyoming's Zerbst Ranch in the 1990s is being studied at the University of Chicago and could redefine understanding of the species. Paleontologist Paul Sereno identified the specimen, known as Rex Jr., as exceptionally important due to preserved gastralia and other rarely found skeletal elements. The fossil, encased in extremely hard rock from the Late Cretaceous Lance Formation, is expected to reveal new information about T. rex anatomy when fully analyzed.