The secret behind the terrifying jaws of deep-sea fish: X-rays reveal joint in their head that allows them to open their mouths 120 degrees wide

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Thousands of feet beneath the ocean’s surface, a ferocious predator equipped with a mouth full of dagger-like teeth dominates an area known as the ‘twilight zone.’

Some barbeled dragonfishes can open their mouths as much as 120 degrees wide to capture their prey, an angle that no other type of fish is capable of.

Now, researchers have discovered an ‘evolutionary marvel’ that suggests the creatures are designed to engulf huge prey, with a unique connection between the skull and vertebral column that gives them unparalleled flexibility.

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Researchers have discovered an ‘evolutionary marvel’ that suggests some barbeled dragonfishes are designed to engulf huge prey, with a unique connection between the skull and vertebral column that gives them unparalleled flexibility

This is the first known example of a complex, flexible head joint in fish, according to the scientists with the Smithsonian’s National Museum of Natural History and the French Muséum national d'Histoire naturelle.

The researchers found that a true functional head joint exists in five groups of barbeled dragonfishes.

Others have instead involved more limited degrees of flexibility, with smaller or fewer vertebrae in the head and neck anatomy.

According to the scientists behind the discovery, the head joint may be an adaptation that evolved for the purpose of ‘engulfing particularly large prey items.’

To determine this, the team examined specimens from collections of the National Museum of Natural History and five other natural history collections around the world.

These creatures typically live between 650 to 3,300 feet deep in the ocean’s ‘twilight zone’ – the mesopelagic zone, making them difficult to study in the wild.

And there, they are a dominant group of predators.

Footage from the study reveals just how wide these fish can open their terrifying mouths, as the scientists manipulate the specimen to demonstrate the functional head joint.

The  team examined specimens from collections of the National Museum of Natural History and five other natural history collections around the world

While barbeled dragonfishes are already known to have a slew of nightmarish characteristics that contribute to their role as predators, the researchers say this adaptation likely adds another to the list.

Their findings are published in the journal Plos One.

‘The arsenal of specialized traits that barbeled dragonfishes have evolved as deep-sea predators – he mouths with dagger-like teeth, distensible stomachs, snake like, black bodies with light producing organs and elaborate chin barbels with bioluminescent tissues – make them ferocious and voracious ambush predators, thus the name dragonfishes,’ said Smithsonian scientist Dave Johnson.

‘We suspect that the head joint adaptation helps these fishes engulf their prey items, since the added flexibility allows them to open their mouths up to 120 degrees wide – an angle that is unmatched in any other group of fishes.’