Unusual Fish with Mouth that Extends to Resemble a Trunk

Found only in rivers and forest ponds in West Africa, this fish has a protruding trunk-like snout that allows it to suck in food or breathe air like a snorkel.

hinge(Fractolemus ansorgii) has what biologists call an expandable proboscis, a tubular structure that can be folded onto the head and extended upward or downward. The lips of the proboscis are lined with tooth-like structures made of keratin, which the fish uses to scrape up algae and other debris.

Alison Evans Researchers at George Washington University in Washington, D.C., used dissection, videography, and CT scans to uncover the jaw's complex structure.

Unlike all other fishes, where the jaw joint is located at the back of the mouth, the hinge mouse's jaw joint is located at the front of the head. The lower jaw is tipped back and pointed toward the throat. The upper jaw is connected to the lower jaw by ligaments and is part of the proboscis. “You can think of the upper jaw more or less hanging onto the skin of the proboscis,” Evans says. This is why the structure can extend far from the head.

Hingemouths offer “a novel mechanical solution to a ubiquitous challenge faced by all fish: how to acquire food in viscous fluid media,” Evans says.

She also observed the fish swimming up to the surface and using its proboscis “like a snorkel” to suck in air. This can be a useful feature in forest pools where oxygen levels can be low.

Scientists aren't sure how hinges evolved because fossil evidence is scant. “The family, fractoremus“The family Quneridae is thought to have originated in the mid-Cretaceous period, but no intermediate forms have yet been found in the fossil record,” says Evans.

“The most important thing for me is that scientists remain curious about the world’s little weirdos,” she says.