I recently read that the only skeleton currently known of Appalachiosaurus was of a juvenile, and the adult animal was significantly bigger.
The juvenile skeleton was about 21 feet long, and the animal likely weighed 1,300 pounds.
This skeleton is about the size of a juvenile Tyrannosaurus rex (using the "Jane" specimen for scale, BMRP 2002.4.1) and, this raises a question in my mind. Is it possible that Appalachiosaurus montgomeriensis would have attained adult sizes close to what we see in adult specimens of Tyrannosaurus rex? And as such, could we classify it as a megatheropod?
Of course there are several other factors in this, such as age, growth stages, and environmental pressure that the animal may have experienced in life.