Appalachiosaurus or “Appalachian lizard” is a genus of tyrannosauroid dinosaur from the Late Cretaceous Period of eastern North America. This was a bipedal predator. Only one juvenile skeleton has been found, representing an individual about 23 feet long and weighing over 1300 pounds. This indicates that an adult would have been much larger. This specimen is the most completely known theropod from eastern North America. It was named after the region from which it was found (the Appalachian Mountains). Only one species is known, A. montgomeriensis, which is named after Montgomery County, Alabama. Both the genus and species were named in 2005 by paleontologists Thomas Carr, Thomas Williamson, and David Schwimmer (not to be confused with the actor of the same name).

The fossils were found in central Alabama from the Demopolis Chalk Formation. This formation dates back to around 77 million years ago. Only parts of the skull and mandible, several vertebrae, part of the pelvis, and hind limbs were recovered. The remains are housed at the McWane Science Center in Birmingham, Alabama. Several characteristics brought scientists to conclude that the remains was of a juvenile, rather than an adult. Appalachiosaurus is much different and more derived than another early tyrannosaur, Dryptosaurus, which was also discovered in eastern North America.