Acrocanthosaurus atokensis dinosaur fossil; photo by Jason Adams on Flickr (noncommercial use permitted with attribution / no derivative works).
Official State Dinosaur of Oklahoma
Oklahoma designated Acrocanthosaurus atokensis as the official state dinosaur in 2006 (Oklahoma recognized another dinosaur as the state fossil in 2000). All State Dinosaurs & Fossils
This fearsome dinosaur had spines on its back and three six-inch claws on each forearm; Acrocanthosaurus atokensis roamed the southern USA during the Middle Cretaceous period (125-112 million years ago).
Paleontologists discovered the first evidence of this dinosaur in the 1940's in Atoka County, Oklahoma (hence the atokensis in its name). They also found part of a skeleton in McCurtain County in the 1980's. Fossil evidence indicates that the Acrocanthosaurus atokensis is similar to the Tyrannosaurus rex, but it is millions of years older.