How to recognise them
Triangular, often with serrated edge.
Sharks are fish with a skeleton made of cartilage, not bone. They evolved around 400 million years ago and have always been top of the marine food chain (except in the Mesozoic, when they were joined by marine reptiles such as plesiosaurs and ichthyosaurs). Some sharks today undertake great migrations, e.g. between South Africa and Australia, and they are usually specialised for life at certain ocean depths, but they cannot live in the deepest waters where some bony fish can survive. Megalodon is one of the most famous fossil sharks - a single tooth can be up to 17 cm long.
A tooth belonging to a 70 cm shark was found in the black mudstones at Fisherstreet, Doolin, by Burren-Cliffs of Moher Geopark Geologist Dr Eamon Doyle in 2015.