The Loch Ness Monster, Nessie, is supposed to be a plesiosaur, the elegant, long-necked marine reptile of the Mesozoic. This species is Plesiosaurus mauritanicus, from the Khouibga plateau in Morocco and is around 70 million years old. Like the mosasaur tooth, I realise this isn't a dinosaur, but it fits best in this category, Apologies to the purists. You can't have Nessie, but you can least have a Nessie tooth...
The teeth themselves vary in length from 4-6cm, and the matrix perhaps 7-8cm across.