'Living fossil' fish haven't evolved in 100 million years

Large gars can grow as large as crocodiles and have armor so tough it helped them survive predatory dinosaurs.

The North American giant gar ( 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 .

Giant anchovies are enormous in size. (Photo: In Fisherman).

With its long snout, thick armor-like scales and sharp teeth, this giant fish is often mistaken for a crocodile. It is the largest known member of an ancient group of ray-finned fish called gars and can grow to about 8 feet (2.4 m) in length.

The giant gar "was truly a prehistoric monster ," according to biologist Jeremy Wade on the show "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 that includes scales made of a super-hard enamel called ganoine , ' explains Wade. ' This armor helps them survive among carnivorous dinosaurs.' The interwoven scales also protect the large gar from threats. When the gar grows to over a meter in length, its only predator is the short-snouted crocodile.

Large gar grow very quickly. They hatch as tiny, poisonous eggs, but can grow to be 2 feet long in their first year. They continue to grow throughout their lives and can live up to 100 years, says Solomon David, an aquatic ecologist at the University of Minnesota.

The giant gar is among the few 'living fossils,' species that have remained virtually unchanged for millions of years. A 2024 study found that the giant gar has the slowest rate of evolution among jawed vertebrates. They evolve so slowly that the giant gar and the alligator gar ( Lepisosteus osseus ), two species separated by 100 million years of evolution, can produce fertile hybrids . Evolution over such a long period of time often results in species that are so divergent that they can never reproduce.

Although the giant gar's sharp teeth can inflict a painful bite, they are ambush predators that feed on crabs, fish, and birds. In the 1930s, the Texas Game Fishing Commission created a device to electrocute the giant gar by firing 200 volts into the water. Today, the giant gar is protected in Florida and restricted for fishing in Texas.