This really looks like the dorsal fin of a dolphin or shark, but thought that the fins consist of cartilage only. Found on a beach in South Devon. Very light and definitely a bone of sorts. If not a fin then what? Birds beak ?

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Hi, Ian. It's always hard to be sure from a single photo, but I am pretty sure that this is the sternum (breast-bone) of a bird. The way you're holding it, it's upside down from how it would be in life: the bird is, if you like, lying on its back, with its head towards the right of the picture.

The next time you eat a chicken, once you've taken off all the breast meat, take a look at the oddly-shaped flat bone that it was attached to. That's the sternum.