Gar

Atractosteus strausi, an Eocene gar from the Messel of Germany

Masillosteus, an Eocene gar from Fossil Butte, Wyoming

Gars are considered to be the only surviving members of the Ginglymodi, a group of bony fish that flourished in the Mesozoic.[14] The oldest known ginglymodians appeared during the Middle Triassic, over 240 million years ago.[15] 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.[16]

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 (Kimmeridgian) 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 prior to the Early Cretaceous.[14][17]

Gars diversified in western North America throughout the Early Cretaceous, forming two tribes; the extinct Cuneatini, which had unusually short snouts, and the Lepisosteini, which contains both extant genera (Atractosteus and Lepisosteus) and the extinct, potentially marine Herreraichthys from the Late Cretaceous of Mexico. 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, and Europe.[17]

Both major tribes of gar and their freshwater genera survived the Cretaceous-Paleogene extinction event, although they remained restricted to North America and Europe after this point. One species (Atractosteus grandei, a relative of the modern alligator gar) is the oldest known animal 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. Both genera of the Cuneatini are known from the Eocene in western North America and Europe, but eventually went extinct. The Lepisosteini show a similar initial distribution and eventual decline, 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.[17]

The following phylogeny of extant and fossil gar genera was found by Brownstein et al. (2022):[17]

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.[21]

As their vascularised swim bladders can function as lungs,[7] 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 (breathing air) 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.[22] This adaptation can be the result of environmental pressures and behavioral factors.[23] As a result of this organ, they are extremely resilient and able to tolerate conditions that most other fish could not survive.

Medial and lateral view of Lepisosteidae pectoral girdle

The gar has paired pectoral fins and pelvic fins, as well as an anal fin, a caudal fin, and a dorsal fin.[24] 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 postcleithrun - 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.[25]

Fin chart for shortnose gar

All the gars are relatively large fish, but the alligator gar (Atractosteus spatula) is the largest. The largest alligator gar ever caught and officially recorded was 8 ft 5 in (2.6 m) long, weighed 327 lb (148 kg), and was 47 in (120 cm) around the girth.[26] Even the smaller species, such as Lepisosteus oculatus, are large, commonly reaching lengths of over 60 cm (2.0 ft), and sometimes much longer.[27]

Alligator gar (Atractosteus spatula)

The largest member of the gar family, the alligator gar (Atractosteus spatula), can measure up to 10 feet long and weigh over 300 pounds.[32][33] Its body and snout are wide and stocky, and it was named "alligator gar" because locals often mistook it for an alligator.[32][34] The species can be found in Texas, Oklahoma, Louisiana, the Mississippi River, Ohio, the Missouri river, and the southern drainages into Mexico.[33][34] Its habitat consists of lakes and bays with slow currents.[33] The gars grow rapidly when young and continue to grow at a slower rate after reaching adulthood.[35] They are deep green or yellow in color.[33][34] Recreational fishing of the alligator gar became popular due to its massive size and its meat is sold for food.[36] Over five decades of overfishing have brought it close to extinction,[34][35] and man-made dams have contributed to this loss by restricting the gar's access to the flood plain areas in which it spawns.[36] Some U.S. states have enacted laws to combat overfishing, and reintroduction programs are being carried out in some states, such as Illinois, where human activity has extirpated the gar.[34][35] Before being released, each gar must meet a length requirement to ensure that it has the best chance of survival in the wild.[37] Some states, such as Texas, restrict the number of gar that may be caught in a day, the season in which they may be caught, and the equipment anglers may use to catch them. Some states also impose a minimum length requirement to prevent gar from being caught at too early an age.[38] Scientists have found that the alligator gar can help maintain ecosystem balance by eating invasive species such as the Asian carp, and their success in a particular area can show scientists that area may also make a suitable habitat for other migratory species.[39]

Lepisosteus platyrhincus

The Florida gar (Lepisosteus platyrhincus) can be found in the Ocklockonee river, Florida, and Georgia,[40][41] and prefers muddy or sandy bottoms with bountiful vegetation.[40][42] It is commonly confused with its cousin, the spotted gar.[40] Uneven black spots cover its head, body, and fins.[40][41] Green-brown scales run along the back of its body, and the scales on its underbelly are white or yellow.[40][43] This coloration, which blends well with the gar's surroundings, allows it to ambush its prey.[40][43] The Florida gar has no ganoid scales on its throat.[40] Female Florida gars grow to lengths between 13 and 34 inches, bigger than their male counterparts.[40][43]

Spotted gar (Lepisosteus oculatus)

The spotted gar (Lepisosteus oculatus) is a smaller species of gar,[32] measuring just under four feet long and weighing 15 pounds on average.[32] Like Florida gars, female spotted gars are typically larger than male spotted gars.[44] This gar has dark spots covering its head, body, and fins.[32] Its body is compact, and it has a shorter snout.[32] It prefers to live in clearer shallow water with a depth of 3–5 meters,[39] and to surround itself in foliage.[42][44] Its habitat ranges from the waters of Lake Michigan, the Lake Erie Basin, the Mississippi River System, and river drainages along the northern coast of the Gulf of Mexico from the Nueces River in Texas east to the lower Apalachicola River in Florida.[44][45] It shares its habitat with the alligator gar, its main predator. These smaller gar live an average of 18 years.[44]

Shortnose gar (Lepisosteus platostomus)

The shortnose gar (Lepisosteus platostomus) is found in the Mississippi River Basin, Indiana, Wisconsin, Montana, Alabama, and Louisiana.[46] It prefers to live in lakes, swamps, and calm pools.[42][46] The shortnose gar takes its name from its snout, which is shorter and broader than that of other gar species.[32][46] Like the longnose gar, it has one row of teeth. The upper jaw is longer than the rest of its head.[46] The shortnose gar is deep green or brown in color, similar to the alligator gar.[32][46] Depending on the clarity of water, spots can be present on the caudal, dorsal, and anal fins.[46] The shortnose gar has a lifespan of 20 years, reaches up to 5 pounds in weight,[47] and grows to lengths of 24–35 inches.[45][47] It consumes more invertebrates than any other gar,[46] and their stomachs have been found to contain higher Asian carp content than any other native North American fish.[39]

Longnose gar (Lepisosteus osseus)

The Longnose gar (Lepisosteus osseus) has a longer, narrower, more cylindrical body,[32][48] and can be distinguished from other species of gar by its snout, which is more than twice the length of the rest of its head.[49][50] It can reach up to 6 feet and 8 inches in length and weigh up to 35–80 pounds.[32][49] Like the shortnose gar, it has only a single row of teeth.[49][50] Unlike its relatives, it enters brackish water from time to time.[42][49] Females are larger and live longer than the male longnose gar.[48][49] Females live 22 years, and males about half as long.[49] There are spots on the head, dorsal, anal, and caudal fins.[32][49][51] Depending on the water clarity, the longnose gar comes in two colors.[49] In clear water, they're a dark deep green color. In muddy waters, it is more brown in color.[49] Edges of the ganoid scales and in between are black.[49][51] These types of gar are occasionally fished by locals, and blamed for eating other fish in the rivers.[48][49] The longnose gar has a large range of territory in North America, into the Gulf of Mexico.[49][51] Located in Florida, Quebec, all Great Lakes except Lake Superior, Missouri, Mississippi, Texas, and northern Mexico.[49][52]