Sperm whale
The toothed whales, comprising the Odontoceti suborder of the cetaceans, are differentiated from the baleen whales by the presence of their teeth. The number of teeth and their function can vary widely between species, with some dolphins having over a hundred teeth in their jaws, while the Narwhal has two functional teeth in its upper jaw which grow into long tusks in males. The tusk is used in feeding, navigation and mating and contains millions of sensory pathways, making it the most neurologically complex tooth known. In contrast, the Sperm whale has up to forty teeth in its bottom jaw and none functional in its upper.