HOLOSTEAN

any member of the subclass, or infraclass, Holostei, a group of archaic, bony fishes represented by the bowfin and the gar of North America. They are one of the three major groups of ray-finned fish (Actinopterygii), the other two being the chondrosteans and the teleosts. Most paleontologists divide the Holostei into the Holosteans proper, which include living and extinct forms, and the Halecostomi, an extinct group. The origin of the Holosteans and the Halecostomi is not fully understood, but it is believed that they arose from advanced chondrostean fishes (the group that includes the sturgeon). The Holostei were particularly abundant and diversified during the Mesozoic Era (65,000,000225,000,000 years ago). Today they are represented by only two living genera, Amia (bowfin) and Lepisosteus (gar). One species of bowfin has been recognized, and some eight species of gar have been described. The gar occurs only in North America and Central America from southeastern Canada to Panama; it is not found west of the Rocky Mountains. The longnose gar (L. osseus) is the most widely distributed species. The gar is primarily a freshwater fish but sometimes ventures into saltwater or brackish water. The so-called alligator gar (L. spatula), one of the largest of freshwater fishes, is particularly abundant in the Everglades region of southern Florida, where it is caught locally as a food fish; it sometimes grows to a length of nearly three metres (10 feet) and may attain a weight of 136 kilograms (300 pounds). The names gar, garfish, and garpike are sometimes applied, especially in Europe, to the needlefishes (Belonidae), which are coastal fishes of warm seas and have very long and slender jaws. These fishes, however, are not closely related to the Holostei. The bowfin, also known as grindle, mudfish, and dogfish, is found in sluggish waters from the Great Lakes to the Gulf of Mexico. It was once common throughout Europe but is now extinct there. Female bowfins reach a length of about 75 centimetres (30 inches) and weigh up to 3.5 kilograms (eight pounds); males are smaller. Bowfins eat all kinds of fish and invertebrates and are sometimes destructive to game-fish populations. Bowfins are seldom caught as food fish. (subclass Holostei), any of a group of archaic, bony fishes represented by the bowfin and the gar of North America. Major characteristics of this subclass include a dermal bone that is free of the upper jaw (maxilla) and attached to the skull only in the vicinity of the nasal chambers, a palate unconnected to the cheek elements, and a heterocercal tail. The scales became rounded (cycloidal) in some groups, but in the primitive condition they were diamond-shaped and had a reduced dentine layer. The bowfin reaches a length of about 75 cm (30 inches) and a weight of 3.5 kg (8 pounds); the males are usually smaller than the females. The alligator gar (Lepisosteus spatula) is the largest living member of the group as well as one of the largest freshwater fish. It can attain a length of 3 m (10 feet) and may weigh up to 136 kg (300 pounds). Living gars are characterized by a long snout that is well endowed with teeth. The body is fusiform, and the dorsal and anal fins, which each have less than 12 rays, are located toward the posterior end of the body. The long snout ends in a beak that may be broad and short, as in the alligator gar, or a long forcepslike arrangement, as found in the long-nose gar (L. osseus). The extinct semionotiforms (Semionotidae), which include the oldest known member of the subclass (Acentrophorus), were fish with short snouts and strong teeth. In some the body was disk-shaped rather than fusiform. The living bowfin has bony plates covering the head, thin cycloidal scales, and a fusiform body. The tail (caudal fin) is lobed, although in extinct forms it was sometimes forked. There are 58 rays in the long, dorsal fin that extends over most of the back. Male bowfins have a dark spot near the tail that is encircled with yellow or orange. In females the entire spot, or at least the coloured border, is lacking. The three extinct orders are the Pachycormiformes, the Pycnodontiformes, and the Pholidophoriformes. Pachycormiforms were fusiform fish with forked tails, large mouths, and well-developed teeth; they generally resembled modern teleosts such as swordfish and mackerel. The pycnodontiforms were unique in having a flat, crushing dentition, although some anterior teeth were incisiform to help in grasping prey. Their bodies were disk-shaped, and they were generally strong, fast swimmers. The pholidophoriforms include those forms closest in structure to modern teleost fish. They differ most strongly from teleosts in the heterocercal (forked) nature of the caudal skeleton. Most living holosteans are limited to fresh water, although some gars may temporarily venture into brackish or marine waters where, however, they do not feed. Gars are able to breathe air, which they obtain while floating at the surface. This ability allows them to inhabit poorly oxygenated waters. Modern bowfins inhabit only sluggishly moving fresh water, although the majority of the extinct forms were marine. The well-developed swim bladder of the bowfin can also be used as a lung, allowing the fish to survive out of water for up to 24 hours. Holostean fish are highly predaceous, feeding on other fish and various invertebrates. Bowfins occasionally decimate local game-fish populations. Bowfins breed in weedy areas along the shore. The male builds a nest and guards the eggs; after they hatch he will guard the fry. The young bowfins are equipped with an adhesive organ at the end of the snout that enables them to hold on to weeds and so remain in one area. Bowfin young grow rapidly and may reach 23 cm (9 inches) in their first year. The gars lay their large, yolk-filled eggs in the spring; these eggs are placed in shallow waters. Long rows of sharp teeth enable the gar fry to capture the fast-swimming minnows that make up their diet. Additional reading S.M. Andrews et al., Pisces, in W.B. Harland et al. (eds.), The Fossil Record: A Symposium with Documentation, ch. 26 (1967), a classification of fish, with first and last occurrences for each family; B.G. Gardiner, A Revision of Certain Actinopterygian and Coelachanth Fishes, Chiefly from the Lower Lias, Bull. Br. Mus. Nat. Hist. (Geol.), 4:239384 (1960), important revised descriptions of early Jurassic fish from Great Britain; E.S. Goodrich, Vertebrata craniata, fasc. 1, Cyclostomes and Fishes, in E.R. Lankester (ed.), A Treatise on Zoology (1909, reprinted 1964), a classic work on the anatomy of fish that is still useful; J.P. Lehman, Actinopterygii, in J. Piveteau (ed.), Trait de palontologie, vol. 4 (1966), a summary of important characteristics of the higher bony fishes, along with their geologic and geographic distributions; D.V. Obruchev (ed.), Fundamentals of Paleontology, vol. 11, Agnatha, Pisces (1967), a summary treatment of all fishes, living and fossil; D.H. Rayner, The Structure and Evolution of the Holostean Fishes, Biol. Rev., 16:218237 (1941), an attempt to relate the various families of holostean fishes mainly on the basis of braincase design; A.C. Weed, The Alligator Gar (1923).