AKA Mesoplodon densirostris, Blainville's whale (named after Henri de Blainville, who first 'described' it, having come across a piece of an upper jaw in 1817), Blainville's beaked whale, Atlantic Beaked Whale, and Tropical Beaked Whale. It is often hyphenated: Dense-beaked whale.
Beaked whales tend to be mysterious, rarely seen animals -- some of them are only know from the corpses that wash up on the beaches. Some of them probably aren't known to us at all. Dense beaked whales are perhaps the best known of the beaked whales. We often see small pods of them and find dead ones washed up on the beaches. But there's a lot we don't know -- we don't know how many of them there might be, how long they live, what their migratory patterns are, among many other things.
The dense beaked whale is probably the beaked whale with the widest distribution, being found all along the Atlantic coast of North America and the Caribbean, and the eastern coast of Australia. There have been less frequent sightings in Europe, Asia, and Africa. They are deep ocean whales, and rarely found close to land except near islands with sharp drop-offs to the seabed. They like warm temperate and tropical waters, and they usually seem to live in waters 700 to 1000 meters deep.
We think that they eat mostly squid and small fish. Pods usually have two to nine individuals (although all strandings have been of single individuals).
They are dark blue, with an even darker dorsal fin and eye patch, and a lighter belly.
The largest recorded whales have been about 4.7 meters long for both males and females.
And, yes, they are called beaked for a reason. The Mesoplodons have protruding teeth, growing up from their lower jaws in a variety of shapes and sizes. The dense beaked whales also have an odd shaped jaw; it's like a porpoise's nose, except that the bottom jaw has grown up on the sides to cup the upper jaw, looking somewhat like a right whale's jaw. This effect is more exaggerated in males than in females. The upper jaw is in the deep saddle of the lower jaw, and in the males the apex of the saddle's arches have two large, triangular teeth. These teeth may be encrusted with sharp barnacles, making them even more dangerous. These are most likely used for hunting food.
Its Latin name, densirostris (from denus and rostrum meaning 'dense beak'), refers to the fact that the jaw of the dense beaked whale is the most dense of any known animal bone.