As life was first struggling to set foot on land in the Late Devonian Period, there was a predator waiting to snatch it back to the depths: the recently discovered Hyneria udlezinye, a toothy prehistoric fish estimated to have reached up to 9 feet long.

It represents the largest monster fish yet uncovered from this period and appears to have lurked in the brackish waters of the modern-day Waterloo Farm site in South Africa, in wait for its prey. An excavation exposed a wall of fossils there in 2016, during road construction, and led to this and a number of other discoveries, including the fossil of an early tetrapod, the massive fish’s likely prey. These early genetic forebears of modern human resembled large salamanders or small alligators and walked on four feet (thus tetrapod).

Finding the Ancient Fish

Thanks to continental drift, the world was a different place some 360 million years ago, when H. udlezinye ruled lakes and estuaries. Waterloo Farm belonged to a large landmass, Gondwana, that reached up from the Antarctic. And the new study argues that the Hyneria genus began here and not on another Devonian continent, Euramerica. And while researchers have identified several of H. udlezinye’s relatives, this one remains the largest, with its long jaws and fangs.

To excavate the discovered skeleton, they picked away at the bones with porcupine quills and removed many fragments of the fish’s impressive skull. After cutting out paper copies of each, they fit them together like a puzzle and revealed a smoothly contoured face that would have slipped through the water like an airplane nose. The researchers told Live Science that the fish’s fins enabled it to bolt up at prey and surprise them.

While other members of the species might have reached 9 feet long, the team estimated the unearthed H. udlezinye at about 6 feet and said it was covered in "elongated scales" that measured up to 3 inches. The skeleton also revealed a larger-than-expected branchial chamber, the area used to cycle water through the gills, suggesting the fish had evolved to linger in oxygen-poor waters while waiting to strike.

This and other giant tristichopterid fishes once terrorized the fresh and brackish waters of the world, with evidence found in modern-day East Greenland, central Russia, Pennsylvania, and New South Wales (locations that were arranged differently during the Devonian Period). But, like many species, they died out during the mass extinction that concluded the period and still invites debate.

An Ancient Monster Fish

Monster fish still swim modern day waters: In 2022, fishermen in Cambodia hauled in a giant freshwater stingray that weighed 661 pounds and measured 13 feet, tail included, making it the largest freshwater fish ever caught. The fish narrowly eclipsed a 646-pound catfish also caught in the Mekong River. But these fish lack the same taste for tetrapods as H. udlezinye.

As our distant ancestors crawled up onto land, they found a rapidly evolving world, according to PBS, including the advent of the first woody plants and "complex plant ecosystems." While the underwater world had been evolving and changing, so had the above-water.

And monsters like H. udlezinye (which means "one who eats others") got left behind.