On Friday, whilst I was in the lovely friendly town of Portaferry catching up with some old friends,  I gave you this mystery object to identify:

Unfortunately my phone seemed reticent to work properly, making it hard to respond to everyone’s questions, so thanks to Debi Linton for fielding some of the questions/suggestions. This object is one of those that is so characteristic in its structure that once you’ve seen one you will probably be able to spot another with ease, even though they have a huge variety of shapes, as pointed out by Benjamin Brooks in his comment (which provides a link to an image hosted by the Oceans of Kansas Paleontology site who incidentally have a mystery object of their own).

If you click on the image I provided you’ll see more detail, which makes it very clear that this is something composed of interlocking units that look like shiny bone. Shiny bone (that looks like a piece of ceramic) usually means bone with an enamel layer, which usually means teeth. These teeth are arrayed in a plate and if you look at the top of the plate you’ll see that it is discoloured, pitted and well worn. Clearly only this top part of the plate has seen much use and that use has been heavy, given the wear.

So why have all the rest of the tooth plate if it isn’t being used? Of course, the rest of the plate will be used, it just hasn’t moved into position yet – so what animal has teeth that move like a conveyor belt and are constantly being replaced? Sharks are the first things to come to my mind, but they don’t tend to have big flat plates, so think of something related to sharks that might need big flat plates for crushing something that very hard, probably marine molluscs.

If you haven’t worked it out already, this is a tooth plate from a ray – in fact this one is from one of the cownose rays, probably Rhinoptera bonasus (Mitchil, 1815) based on the seven series of teeth. There is an excellent description of the cownose ray by the Florida Museum of Natural History if you want to know more.

Finally I’d like to congratulate everyone who had worked out that this was a ray tooth plate and who dropped hints rather than give it away – the powerpack for Dan Dare’s raygun by Dave Godfrey was nice and I liked Robert Grant‘s You are all Batty, which is a nice reference to the Batoidea, the group of cartilaginous fish that contains the rays. I must admit that Tim Jones‘ Fishes with piles has left me puzzled, but I expect that’s more to do with my mental state after only arriving back from Northern Ireland in the small hours of the morning.