Gar


Gars are an ancient group of ray-finned fish in the family Lepisosteidae. They 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, though extinct members of the family were more widespread. They are the only surviving members of the Ginglymodi, a clade of fish which first appeared during the Triassic period, over 240 million years ago, and are one of only two surviving groups of holosteian fish, alongside the bowfins, which have a similar distribution.
Gars have elongated bodies that are heavily armored with ganoid scales, 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 is the largest; the alligator gar often grows to a length over and a weight over, and specimens of up to in length have been reported. Unusually, their vascularised swim bladders can function as lungs, 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.

Etymology

The name "gar" was originally used for a species of needlefish found in the North Atlantic and likely took its name from the Old English word for "spear". 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. 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". Atractosteus is similarly derived from Greek, in this case from atraktos, meaning ''spindle.''

Evolution

Evolutionary history

Gars are considered to be the only surviving members of the Ginglymodi, a group of bony fish that flourished in the Mesozoic. The oldest known ginglymodians appeared during the Middle Triassic, over 240 million years ago. They exhibit the slowest known rate of molecular evolution among all jawed vertebrates, with DNA evolving up to a thousand times more slowly than in other groups, which has consequently reduced their rate of speciation. The closest living relatives of gars are the bowfin, with the gars and bowfin together forming the clade Holostei; both lineages diverged during the Late Permian.
The closest extinct relatives of gar are the Obaichthyidae, an extinct group of gar-like fishes from the Early Cretaceous of Africa and South America, which likely diverged from the ancestors of true gars during the Late Jurassic. The oldest anatomically modern gar is Nhanulepisosteus from the Upper Jurassic of Mexico, around 157 million years old. Nhanulepisosteus inhabited a marine environment unlike modern gars, indicating that gars may have originally been marine fish prior to invading freshwater habitats before the Early Cretaceous. Although most succeeding gar fossils are known from freshwater environments, at least some marine gars are known to have persisted into the Late Cretaceous, with the likely marine Herreraichthys known from Mexico and the definitely marine Grandemarinus known from Morocco.
Gars diversified in western North America throughout the Early Cretaceous. Atractosteus and Lepisosteus had already diverged by the end of the Early Cretaceous, about 105 million years ago. From western North America, gars dispersed to regions as disparate as Africa, India, South America and Europe, and fossil remains of gars were widespread worldwide by the end of the Cretaceous.
Several different gar genera survived the Cretaceous–Paleogene extinction event, although they remained restricted to North America and Europe after this point. One species is the oldest known articulated vertebrate specimen of the Cenozoic, with one fossil specimen dated to just a few thousand years after the Chicxulub impact, indicating a rapid recovery of freshwater ecosystems. Two short-snouted gar genera, Masillosteus and Cuneatus, are known from the Eocene in western North America and Europe, but disappear shortly afterwards. Lepisosteus and Atractosteus show a similar initial distribution and eventual contraction, but both genera dispersed to eastern North America prior to their disappearance from western North America and Europe, with Atractosteus also dispersing further south to the Neotropics. Eastern North America has since served as a vital refugium for gars, with Lepisosteus undergoing a diversification throughout it.

Phylogeny

The following phylogeny of extant and fossil gar genera was found by Brownstein et al. :
A slightly different phylogeny was found by Cooper et al :

Distribution

Fossils indicate that gars formerly had a wider distribution, having been found on every continent except Australia and Antarctica. 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. A few populations are also present in the Great Lakes region of the United States, living in similar shallow waters.

Anatomy

Scales

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.

Swim bladder

As their vascularised swim bladders can function as lungs, most gars surface periodically to take a gulp of air, doing so more frequently in stagnant or warm water when the concentration of oxygen in the water is low. Experiments on the swim bladder has shown that the temperature of the water affects which respiration method the gar will use—aerial or aquatic. They increase the aerial breathing rate as the temperature of the water is increased. Gars can live completely submerged in oxygenated water without access to air and remain healthy while also being able to survive in deoxygenated water if allowed access to air. This adaptation can be the result of environmental pressures and behavioral factors. As a result of this organ, they are extremely resilient and able to tolerate conditions that most other fish could not survive.

Pectoral girdle

The gar has paired pectoral fins and pelvic fins, as well as an anal fin, a caudal fin, and a dorsal fin. The bone structures within the fins are important to study as they can show homology throughout the fossil record. Specifically, the pelvic girdle resembles that of other actinopterygians while still having some of its own characteristics. Gars have a postcleithrum—which is a bone that is lateral to the scapula, but do not have postpectorals. Proximally to the postcleithrum, the supracleithrum is important as it plays a critical role in opening the gar's jaws. This structure has a unique internal coracoid lamina only present in the gar species. Near the supracleithrum is the posttemporal bone, which is significantly smaller than other actinopterygians. Gars also have no clavicle bone, although elongated plates have been observed within the area.

Morphology

All the gars are relatively large fish, but the alligator gar is the largest. The largest alligator gar ever caught and officially recorded was long, weighed, and was around the girth. Even the smaller species, such as Lepisosteus oculatus, are large, commonly reaching lengths of over, and sometimes much longer.

Ecology

Gars tend to be slow-moving fish except when striking at their prey. They prefer the shallow and weedy areas of rivers, lakes, and bayous, often congregating in small groups. They are voracious predators, catching their prey in their needle-like teeth with a sideways strike of the head. They feed extensively on smaller fish and invertebrates such as crabs. Gars are found across much of the eastern portion of North America. Although gars are found primarily in freshwater habitats, several species enter brackish waters and a few, most notably Atractosteus tristoechus, are sometimes found in the sea. Some gars travel from lakes and rivers through sewers to get to ponds.

Species and identification

The gar family contains seven extant species, in two genera. This list also includes definitively known fossil taxa, common names for which are based on Grande :
Family Lepisosteidae
  • Genus †Nhanulepisosteus Brito, Alvarado-Ortega & Meunier, 2017
  • Genus †Britosteus Martinelli et al 2025
  • Genus †Masillosteus Micklich & Kappert, 2001
  • Genus †Cuneatus Grande, 2010
  • Tribe Lepisosteini
  • *Genus †Herreraichthys Alvarado-Ortega et al 2016
  • *Genus †Grandemarinus Cooper et al 2023
  • *Genus †Oniichthys Cavin & Brito, 2001
  • * Genus Atractosteus Rafinesque, 1820
  • ** †Atractosteus atrox
  • ** †Atractosteus grandei Brownstein & Lyson, 2022
  • ** †Atractosteus messelensis Grande, 2010
  • ** †Atractosteus simplex
  • ** Atractosteus spatula
  • ** Atractosteus tristoechus
  • ** Atractosteus tropicus Gill, 1863
  • * Genus Lepisosteus Linnaeus, 1758
  • ** †Lepisosteus bemisi Grande, 2010
  • ** †Lepisosteus indicus
  • ** Lepisosteus oculatus Winchell, 1864
  • ** Lepisosteus osseus
  • ** Lepisosteus platostomus Rafinesque, 1820
  • ** Lepisosteus platyrhincus DeKay, 1842