Nice job, lots of good figures and a real ceratopsid specimen, no doubt about that.
Here are some suggested edits/additions regarding geology, taphonomy, and paleogeography. Mainly I am interested in how we know this specimen derives from the landmass of Appalachia, rather than being a bloat-and-float carcass derived from Laramidia.
OWL CREEK GEOLOGY
Can we have some more information on the geology of the Owl Creek Fm. This is important as I understand the formation is marine (Line 51). Is it entirely marine? Are any parts shallow marine (ie close to an Appalachia shoreline?), or even terrestrial?. This is implied from some neritic fossils, but it could be stated more explicitly. What evidence is there that we are near to the Appalachian landmass?
Is it possible to include a short section discussing how we might be sure that this tooth is not derived from a dinosaur carcass that originated on Laramidia, and floated out to the coast of Appalachia (if indeed the Owl Creek Fm was deposited near the paleo coastline). Any documentation of paleocurrents etc? It isn't clear to me why this specimen should be considered as from Appalachia since it was collected from marine sediments and (see below) the western coastline of Appalachia is unknown.
Would be nice to see a few more references on the Late Maastrichtian regression of the seaway. What evidence has been presented that land bridges occurred between Laramidia and Appalachia? Recent work (e.g. Boyd & Lillegraven, 2011, which includes good discussion and references) has suggested that in the northern states at least the seaway remained intact through the K-Pg boundary. Slattery et al (2016, referenced in the current work) states that the eastern coast of the seaway is "completely unknown" during the Campanian through Danian, and notes that there is no evidence to suggest a land bridge between Laramidia and Appalachia before the K-Pg boundary, adding that presence of marine taxa with arctic & gulf affinities supports a continuous connection through the Late Maastrichtian (see. p47-48). Admittedly, preserved evidence is sparse, and Slattery et al. does say that no faunal mixing (dinosaurs) is known to have occurred in the Maastrichtian, as might be expected based on the presence of a land bridge; hence the new specimen is of great importance if it can be demonstrated that it originated on the Appalachia landmass, and not as bloat and float from Laramidia.
-I suspect it is probably not possible to know on which subcontinent the specimen originated, but in which case documenting the geology of the Owl Creek, and perhaps mentioning the possibility of the bloat-and-float scenario, might be worthwhile.
e.g. (line numbers)
Line 46: Should have a reference in there for the regression of the seaway.
Line 71-73: Give references for the fossils found in the Paleocene and Cretaceous units, esp. the dinosaurs given the subject matter of the paper.