This tooth is from Harding County, Hell Creek formation. Now--it is tiny.
1mm long, so is the smallest tooth I own by far, but it has quite clear serrtations that can be photographed. It came with a few others and this one stands out because of its fatness and squatness (most of the others are long, relatively speaking) I am wondering if possibly, maybe, hopefully .... I may have a baby/infant Rex? Now, unfortunately, the base is a bit thin--but could that be because of the size of the tooth?
It's quite an unusual one and hope it can be ID'd