LEPISOSTEIFORMES

There are only 7 living species of gars classified in two genera: Lepisosteus (4 species) and Atractosteus (3 species). All species of gars alive today are found in the fresh and brackish waters of North and Central America and Cuba (occasionally, some species enter coastal marine waters). They are most commonly found in sluggish backwaters and swamps and can be locally abundant. The Alligator Gar, Atractosteus spatula, is one of the largest fish in the freshwaters of North America, surpassed only by the Lake Sturgeon (Acipenser fulvescens).

Acipenser ruthenus (cleared and stained), juvenile (Courtesy P. Bartsch)

As a group, gars have an elongate, cylindrical body with heavy overlapping ganoid scales that articulate with one another through a peg-and-socket arrangement to form a heavy, impenetrable scale jacket. The dorsal and anal fins are positioned far back on the body, and they appear to “hang” in the water column, using their paired and median fins to slowly row themselves around.

Gars typically have an elongate, duckbill-like snout with extremely sharp, needle-like teeth, and can quickly slash their jaws sideways to capture their prey, which consists largely of smaller fishes but may also include aquatic insects and other small organisms. Within gars however, there is substantial variation in the shape of the snout, from relatively short and broad, as in the Alligator Gar, to extremely long and narrow, as in the Longnose Gar (Lepisosteus osseus). Some fossil gars even have large, molariform teeth set in very short jaws, which appear to have been used for crushing hard-shelled invertebrate prey.

The fossil record of gars extends back to Late Cretaceous. Fossil gars have been found in Africa, India, North America and South America, and display a wide range of morphological diversity. Gars have been most commonly identified in the fossil record based on their distinctive scales and vertebral elements (gars are unique among ray-finned fishes in having opisthocoelus vertebrae, or vertebral centra with a posteriorly concave surface). However, there are also a large number of fossil gar taxa known from complete or nearly complete skeletons. The anatomy and phylogenetic relationships of fossil and living gars is the subject of a current study by Grande and Bemis.