Appalachiosaurus (; "Appalachian lizard") is a genus of tyrannosaurian theropod dinosaur from the Late Cretaceous period of what is now eastern North America. It was a basal member of the Eutyrannosauria clade meaning it was rather close in relation to the true tyrannosaurids such as Tyrannosaurus. Like most theropods, it was a bipedal predator. Only a juvenile skeleton has been found, representing an animal approximately 6.5m (21.3feet) long and weighing 623kg (1,373lb), which indicates an adult would have been significantly larger.
Fossils of Appalachiosaurus were found in central Alabama's Demopolis Chalk Formation. This formation dates to the middle of the Campanian age of the Late Cretaceous, around 77 million years ago.[1] Fossil material assigned to A. montgomeriensis is also known from the Donoho Creek and Tar Heel-Coachman formations of North and South Carolina in 2007.[2]
The type specimen was found by Auburn University geologist David King in July 1982.[3] This dinosaur was named after the region of the eastern United States known as Appalachia, which also gave its name to the ancient island continent where Appalachiosaurus lived. Both are named after the Appalachian Mountains. The generic name also includes the Greek word sauros ("lizard"), the most common suffix used in dinosaur names. There is one known species, A. montgomeriensis, which is named after Montgomery County, Alabama. Both the genus and species were named in 2005 by paleontologists Thomas Carr and Thomas Williamson.
The juvenile specimen of Appalachiosaurus measures approximately long and .[1] [4] So far, it is only known from partial remains, including parts of the skull and lower jaw, as well as several vertebrae, parts of the pelvis, and most of both legs. These remains are housed at the McWane Science Center in Birmingham, Alabama. There are several open sutures between bones of the skull, indicating that the animal was definitely a juvenile. Several of its bones are crushed, but the specimen is still informative and shows many unique characteristics. Several of these have been identified in the skull and the foot claws show an unusual protrusion on the end closest to the body. A row of six low crests lines the top of the snout, similar to those of the Asian Alioramus, although most tyrannosaur species exhibit ornamentation to varying degrees on top of their snout and brows. The only remains found are from a juvenile, meaning that the size and weight of an adult is unknown. Appalachiosaurus is significantly different and more derived than another eutyrannosaur from eastern North America, Dryptosaurus.
The arms of Appalachiosaurus are poorly known. Large tyrannosaurids are characterized by proportionally small arms and hands with two functional fingers. Although some reports of a humerus are ascribed to Appalachiosaurus, no arm material is actually known.[5] Early reconstructions gave it long arms with three large fingers, but they are now thought to have been much shorter and have only two fingers. Museum mounts have been corrected accordingly, though other locations still support the former theory.[6] Appalachiosaurus had a bone-crushing bite force of around 32,500 newtons, or 7,193 pounds per square inch. [7]
The only known specimen of Appalachiosaurus was complete enough to be included in phylogenetic analyses using cladistics. The first was performed before the animal had even been named and found Appalachiosaurus to be a member of the Albertosaurinae subfamily of Tyrannosauridae, which only includes Albertosaurus and Gorgosaurus.[8] The original description also included a cladistic analysis, finding A. montgomeriensis to be a basal tyrannosauroid outside of Tyrannosauridae.[1] However, Asian tyrannosaurs, like Alioramus and Alectrosaurus, were excluded, as was Eotyrannus from England. Earlier tyrannosaurs, such as Dilong and Guanlong, had not been described at the time this analysis was performed. These exclusions may have a significant effect on the phylogeny.
Below is a cladogram published in 2013 by Loewen et al..[9]
Two vertebrae of the tail were found to be fused together, which is possibly a result of new bone growth following some sort of minor or traumatic injury.