Yikes! I'm thinking that this was probably the lower jaw of a shark, the type of shark I'm not sure, but seeing all of those layers of teeth make me feel like surely it a ferocious one! Up close one can see (and feel!) the razor-like edges of each tooth, four layers deep. I know that this came from a New England prep school biology department, where it lived for a long time. 

9 1/2" l x 5" w x 2 3/4" d and in good condition. There is one patch of a bit of loss along an outside edge of the bone on one side, as documented, which make it a bit delicate. It seems that it could be hung from the jointed top, just resting on a nail, if desired, or else just set somewhere.