Reptile and mammoth teeth

From left to right: Spinosaurus tooth from the Kem Kem Beds of Morocco, Alligator tooth from the St. Marks River in Florida, unidentified reptile tooth sold to me as a mosasaur tooth (presumably from Morocco), but as you can see, it looks nothing like one, an actual mosasaur tooth from Morocco, and a chunk of mammoth tooth from the North Sea.