Curious collections: two-tusked narwhal
Marine mammal expert Richard Sabin takes us through what scientists know - and don't know - about narwhals, also known as unicorns of the sea.
Ask a world-leading scientist a silly question, get a fascinating answer.
Does the Museum have any unicorns?
While Richard confirms there are no unicorns in the Museum, the collections do include a solid representative sample of narwhals.
The collection includes a rare, two-tusked specimen and one of two animals that travelled all the way from the Arctic Circle to British waters in 1949.
Unicorns of the sea
Narwhals (Monodon monoceros) are toothed whales that live primarily in Arctic coastal waters and inlets. Male and female narwhals only have two teeth which are both found in the upper jaw.
The male's iconic, spiralling tusk is in fact a canine tooth, and it can grow up to three metres in length.
Collected by Inuit and traded to gullible Europeans as actual unicorn horn, narwhal tusks were once a highly sought-after commodity.
It's also possible that the spiral shape played a big part in informing the way unicorn horns have been depicted from medieval times to today.
'There is lots of evidence to suggest that the mythology which surrounds the unicorn could be based on the appearance of narwhal tusks that were traded down from the Arctic into Europe,' says Richard.
'Seeing a tusk like that in isolation from anything else, you can imagine you'd be wondering what kind of beast it came from.'
Narwhals belong to a family called Monodontidae, which contain two species: the narwhal and the beluga (or white whale).
Why do narwhals have tusks?
Scientists are still on the fence about the evolutionary purpose of narwhal tusks, however there are a number of prevailing theories about their purpose.
Richard says, 'Although the tusks don't appear externally in the female of the species, if you look inside the upper jaw and remove sections of bone as we have done with a few skulls in our collection, you can see two small, un-erupted tusks. They might serve a purpose we're not currently aware of, but they certainly have no external function.
'In the majority of cases, erupted tusks appear only in males and the left-side tusk is the one that tends to emerge, growing with a left-handed spiral.'
'Very occasionally we see a rare case where the right tusk will also emerge and you'll have quite a freakish-looking double-tusker, but it's a very uncommon occurrence.'
A very sensitive tooth
A study from 2014 , showed that the surface of the tusk is actually covered in open pores leading to a central pulp core full of thousands of exposed nerve endings and blood vessels.
'In a human, that would not only be unpleasant but excruciatingly painful. With a narwhal, it appears that their tusk has some kind of large-scale sensory function.
'It could be that it allows them to detect changes in water temperature, salinity or water pressure. There's a whole range of factors that we still need to quantify.'
Other theories are that male narwhals might use their tusks as a kind of pick to break through or break up channels in the ice, or that the size of the tusk is a visual indicator used by females for mate-selection.
Clues in wear patterns
According to Richard, a slanting wear pattern frequently found on the tips of tusks could offer an important clue to one of their uses.
'Some of the tusks in our collection show an oblique wear pattern which could have been caused by a number of different behaviours, such as spearing their prey,' he says.
There has also been a lot of discussion around the idea that male narwhals appear to use their long, lance-like tooth to intimidate each other, emerging side by side in the water and crossing tusks in a kind of combat.
Many adult males wear duelling scars from these encounters and some animals have been found with tusk tips lodged in their skull.
Recent drone footage has shed some light on the feeding practices of male narwhals. They were observed using their tusk to tap fish and stun them - similar to how killer whales corral fish and then stun them by slapping them with their tails.
'Like killer whales and most toothed cetaceans, narwhals are suction feeders, so you see them tapping the fish and sucking them in, swallowing them whole. It could be that this is one of the main functions of the tusk, or simply an opportunistic benefit the males have realised and incorporated into their feeding behaviour' says Richard.
'Drone footage is enlightening because the drones are able to collect data in a way which is largely unobtrusive and they don't seem to affect the behaviour of the animals that are studied.'
Scientists have lots more to learn about narwhals, and drones could offer a great way to safely continue our observations. For now, we still don't know what led to this unique, gender-specific use of the tusk.
A narwhal in the Thames
Among the narwhals in the collection is an example found a long way from its Arctic home. In 1949, two narwhals (one male and one female) were recorded by the national cetacean strandings programme, originally set up by the Museum which has been monitoring British coastlines since 1913.
The female was found stranded in the River Medway in Kent, while the male made it all the way into the lower reaches of the Thames. The female was collected and incorporated into the Museum's research collection.
'Both strandings are what we call extra-liminal records as they were found way outside of the Arctic waters, where you would usually expect to find narwhals,' Richard says.
'It could be that these two animals were suffering from disease or became disorientated, losing their way and growing weaker as they travelled further south. Perhaps they were pursued by killer whales at some point, we just don't know.'
Visit the Museum
You can see the two-tusked narwhal on the mezzanine level of the Mammals gallery.