The Alligator Gar (Atractosteus spatula) is a ray-finned euryhaline fish related to the bowfin in the infraclass Holostei. It is the largest species in the gar family, and among the largest freshwater fishes in North America. The fossil record traces its existence back to the Early Cretaceous over a hundred million years ago.
Gars are often referred to as "primitive fishes", or "living fossils" because they have retained some morphological characteristics of their earliest ancestors, such as a spiral valve intestine which is also common to the digestive system of sharks, and the ability to breathe both air and water. Their common name was derived from their resemblance to the American alligator, particularly their broad snout and long, sharp teeth. Anecdotal evidence in several scientific reports suggest that an alligator gar can grow up to 10 feet (3.0 meters) in length, but in 2011, the largest alligator gar ever caught and officially recorded was 8 feet 5 1/4 inches (2.572 meters) long, weighed 327 pounds (148 kilograms), and was 47 inches (120 centimeters) around the girth.
The body of an alligator gar is torpedo-shaped, usually brown or olive fading to a lighter gray or yellow ventral surface. Their scales are not like the scales of other fishes; rather, they are ganoid scales which are bone-like, diamond-shaped scales, often with serrated edges, and covered by an enamel-like substance. Ganoid scales are nearly impenetrable and are excellent protection against predation. Unlike other gar species, the upper jaw of an alligator gar has a dual row of large, sharp teeth which are used to impale and hold prey. Alligator gar are stalking, ambush predators, primarily piscivores, but they will also ambush and eat waterfowl and small mammals they find floating on the water's surface.