‘Living fossil’ fish have not evolved for 100 million years

North American giant catfish (Atractosteus spatula) lives in rivers, reservoirs, and coastal bays from the southwestern states of the United States, to Veracruz, Mexico. They specialize in eating crabs, fish, birds, mammals, turtles and carrion, according to Live Science.

With a long snout, thick armor-like scales and two sharp teeth, this giant fish is often mistaken for a short-snouted crocodile. They are the largest known species of the ancient ray-finned fish group called gar and can grow to about 2.4 m long.

The giant snakehead fish “is truly a prehistoric monster,” according to biologist Jeremy Wade on “River Monsters.” Fossils show they existed 100 million years ago during the Cretaceous period (66 – 145 million years ago), when dinosaurs roamed the Earth.

“Their survival is partly due to a unique defense system consisting of scales made of super-hard enamel called ganoine,” explains Wade. “This armor helps them survive among carnivorous dinosaurs.” The hard, interlocking scales also protect large snakehead fish from threats. When large snakehead fish are more than a meter long, their only enemy is the short-snouted crocodile.

Large snakehead fish grow very quickly. They are born as tiny poisonous eggs, but can grow up to 0.6 m long in the first year. They continue to grow throughout their lives and can live up to 100 years, according to Solomon David, an aquatic ecologist at the University of Minnesota.

Giant snakehead fish are among the few “living fossil” species, species that have remained largely unchanged for millions of years. A 2024 study found that giant flathead fish have the slowest evolutionary rate among jawed vertebrates. They evolved so slowly that giant flatfish and rocket crocodile (Lepisosteus osseus), two species separated by 100 million years of evolution can still produce viable hybrids. Evolution over such long periods of time often creates species that diverge so strongly that they can never reproduce.

Although the sharp teeth of giant snakeheads can cause a painful bite, they are ambush predators that feed on crabs, fish and birds. In the 1930s, the Texas Recreational Fishing Commission created a device to electrocute large village fish by firing 200 volts into the water. Today, large village fish are protected in Florida and restricted in Texas.