Gars are members of the family Lepisosteidae, which are the only surviving members of the Ginglymodi, an ancient holosteian group of ray-finned fish, which first appeared during the Triassic, over 240 million years ago. Gars comprise seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine waters of eastern North America, Central America and Cuba in the Caribbean,[2][3] though extinct members of the family were more widespread. Gars have elongated bodies that are heavily armored with ganoid scales,[4] and fronted by similarly elongated jaws filled with long, sharp teeth. Gars are sometimes referred to as "garpike", but are not closely related to pike, which are in the fish family Esocidae. All of the gars are relatively large fish, but the alligator gar (Atractosteus spatula) is the largest; the alligator gar often grows to a length over 2 m (6.5 ft) and a weight over 45 kg (100 lb),[5] and specimens of up to 3 m (9.8 ft) in length have been reported.[6] Unusually, their vascularised swim bladders can function as lungs,[7]and most gars surface periodically to take a gulp of air. Gar flesh is edible and the hard skin and scales of gars are used by humans, but gar eggs are highly toxic.
The name "gar" was originally used for a species of needlefish (Belone belone) found in the North Atlantic and likely took its name from the Old English word for "spear".[8] Belone belone is now more commonly referred to as the "garfish" or "gar fish" to avoid confusion with the North American gars of the family Lepisosteidae.[9] Confusingly, the name "garfish" is also commonly used for a number of other species of the related genera Strongylura, Tylosurus, and Xenentodon of the family Belonidae.
The generic name Lepisosteus comes from the Greek lepis meaning "scale" and osteon meaning "bone".[10] Atractosteus is similarly derived from Greek, in this case from atraktos, meaning arrow.[11]
Gars are considered to be the only surivivng members of the Ginglymodi, a group of bony fish that flourished in the Mesozoic.[1] The oldest known ginglymodians appeared during the Middle Triassic, over 240 million years ago.[12] The closest living relative of gars is the bowfin, with the gars and bowfin together forming the clade Holostei. The oldest known fossils of anatomically modern gars are from the Upper Jurassic (Kimmeridgian) of Mexico, around 157 million years old.[1]
Fossils indicate that gars formerly had a wider distribution, having been found on every continent except Australia and Antarctica.[1] Living gars are confined to North America. The distribution of the gars in North America lies mainly in the shallow, brackish waters off of Texas, Louisiana, and the eastern coast of Mexico, as well as in some of the rivers and lakes that flow into them.[13][14] A few populations are also present in the Great Lakes region of the United States, living in similar shallow waters.[15]
Gar bodies are elongated, heavily armored with ganoid scales, and fronted by similarly elongated jaws filled with long, sharp teeth. Their tails are heterocercal, and the dorsal fins are close to the tail.[16]