An ancient amphibian that roamed the earth and its lakes 210 million years ago may have had the world’s most bizarre bite — rather than opening its mouths by lowering its bottom jaw, like other vertebrates, Gerrothorax pulcherrimus would raise its upper jaw.

Or, according to Reuters, “it lifted the top of its head in a way that looked a lot like lifting the lid of a toilet seat”.

Palaeontologist Farish Jenkins, of Harvard University, and his colleagues published their finding on this abnormal amphibian’s upside-down bite in the Journal of Vertebrate Paleontology.

“It’s the ugliest animal in the world,” Jenkins told Reuters.

While this seems like harsh judgment for a fossil, Jenkins’s description of G. pulcherrimus in a Society of Vertebrate Paleontology press release doesn’t exactly describe a cute cuddly amphibian that you’d like to spot in the local pond. “With their very flat, heavily armoured bodies, short, stubby limbs, massive shoulder girdles and well-developed gills, these amphibians are an oddity by any measure,” he says.

And, the 1-metre long G. pulcherrimus used to lurk at the bottom of lakes awaiting unsuspecting prey, Jenkins and colleagues speculate. Their bizarre bite was “perfect for a bottom-dwelling ambush predator,” says Jenkins.

G. pulcherrimus fossils have been found in Greenland, Western Europe and Scandinavia, leading co-author Anne Warren, a palaeontologist at La Trobe University in Melbourne, Australia, to suggest that “their unique structure was hugely successful”. The last descendents of the Gerrothorax died out some 200 million years ago, however, so it can’t have been that successful.

Image: reconstruction of head lifting during feeding / drawing by L. L. Meszoly, composition by D. Smiley