Bones in Alabama

The bones, finally put into a composite here, that were described by Carr, Williamson, and Schwimmer, were a good portion, compared to some type specimens, of a dinosaur. Enough, obviously, to distinguish separating characters and warrant the creation of a new genus for the remains. This graphic is a little backwards compared to what we normally see when we are looking at a "discovered bone" skeleton. Typically the shaded portions are the bones that have been found but in this illustration it is the white bones that have been discovered and used to name the new species. Carr and his associates decided that, in this description of the remains, Appalachiosaurus is not as basal, i.e. more derived or more "tyrannosaur-like", than Dryptosaurus and thus should be given a seat further up the family tree; though probably still in the trunk and not out on a branch end. The legs and skull are fairly well preserved, the skull not as much obviously, but they certainly make up enough evidence of individuality and separation from other tyrannosaurs. The vertebrae play a part in this as well, and we shall examine that in more detail in time.

Borrowed from Mark Wildman, I assume it is is his photo

The most interesting debate that I can start with, without going into this that and another discussion within the naming paper, is the assumption of hands. Tyrannosaurs have the unenviable position of typically being presented with a lack of digits. In foot related issues this is not a big deal (many dinosaurs and birds alike are "missing" digits on their feet), but when we come to the hands this can be a family tree issue; I know it can be with the feet as well but let us ignore that for today for the sake of argument. Tyrannosaurs as we think of them are missing digits on the hand, specifically digits 4 and 5 without about half of the bones of the third digit ending as a small metacarpal that does not become a fully formed finger/claw. Why is this important? The arms and hands of Appalachiosaurus, to this point have not been recovered. This leads to multiple interpretations of the hands. Were the hands formed as they were, basally, in Dryptosaurus with digits 1-3 expressed as large clawed fingers or were they like those of later tyrannosaurs with digits 1 and 2 expressed as fingers with the third digit being represented by a small section of bone and digits 4 and 5 non-apparent. Perhaps it was intermediate, with three fingers but digit 3 significantly reduced. One can see the multitude of possibilities. For now, at least, the displayed skeleton (in the McWane Science Center of Birmingham, AL) possesses three fingers like Dryptosaurus.

Regardless of the fingers represented, Appalachiosaurus is a tyrannosaur, and that means it was a big theropod. The island continent of Appalachia consisted of, basically, the formed Appalachian mountains bordering the Atlantic Ocean, the beginning of the Great Plains bordering the Western Interior Sea (I would be writing about 200 feet underwater if the geography were the same today!) and stretching from the Arctic circle and Greenland to about middle Alabama/Mississippi/Georgia in the extreme southern reach of the continent. This Appalachiosaurus, then, was found at the southern reach of the continent and Dryptosaurus lived along what would have been the eastern shores. There was still a lot of other land to roam for these two theropods which allowed them to grow to larger sizes than other island dwelling dinosaurs that suffered from the effects of insular dwarfism; a phenomenon that I find fascinating and adorable. The specimen described is thought to be a juvenile, due to unfused skull elements discovered, and would be about the size in the illustration. Adults could have, and most likely did, grown to much larger sizes.