Tyrannosaurus rex Osborn, 1905 theropod dinosaur skull (left lateral view) from the Cretaceous of South Dakota, USA (replica of skull of "Sue" specimen, public display, FMNH PR 2081, Field Museum of Natural History, Chicago, Illinois, USA).

Theropod were small to large, bipedal dinosaurs. Almost all known members of the group were carnivorous (predators and/or scavengers). They represent the ancestral group to the birds, and some theropods are known to have had feathers. Some of the most well known dinosaurs to the general public are theropods, such as Tyrannosaurus, Allosaurus, and Spinosaurus.

Tyrannosaurus rex is the most famous theropod dinosaur. It was a large bipedal predator in western North America 65 to 68 million years ago, during the latest Cretaceous (Maastrichtian Stage). The most famous specimen is FMNH PR 2081, nicknamed “Sue”, housed at Chicago’s Field Museum of Natural History. The specimen was stolen from its discoverers by the American government (greed always brings out the worst in everyone) and was eventually auctioned for $8,362,500. It was bought by McDonald’s and Disney on behalf of Chicago’s Field Museum, where the actual skeleton is on permanent display. In addition to the skeleton, two complete replicas exist: one owned by McDonald’s and one owned by Disney.

FMNH PR 2081 is 42 feet long (from snout to tail tip) and stands 13 feet high (base of feet to top of hip). The skeleton is about 90% complete, lacking several neck bones, some portions of the thoracic vertebrae, portions of the distal-most tail vertebral elements, most of the left arm, and all of the left foot. This individual was an old adult of 28 years. Several deformities are present on the skeleton, representing bone lesions or healed breaks.

Classification: Animalia, Chordata, Vertebrata, Dinosauria, Saurischia, Theropoda, Allosauria, Tyannosauridae, Tyrannosaurinae

Stratigraphy: Hell Creek Formation, Maastrichtian Stage, upper Upper Cretaceous