ACTINOPTERYGII- infraclasses Chondrostei, Holostei and Teleostei

CHONDROSTEI

Most chondrostean species lived during the late Palaeozoic. There are only two chondrostean lineages that survive today, the paddlefish of Canada and China and the sturgeons of Europe, Asia and Canada.

Both lineages have secondarily lost a number of their actinopterygian characters:


Paddlefish

Lake sturgeon

The extant forms are currently endangered as a result of habitat degradation and overfishing for their flesh and their eggs (Sturgeons' caviar).

HOLOSTEI

The holosteans arose in the Permian. They succeeded the Chondrosteans as the dominant fishes in the middle of the Mesozoic. Even fewer holosteans than chondrosteans survive today. These include the bowfin Amia of eastern Canada, and seven species of garpikes (Lepisosteus and Atractosteus) from North and Central America.


Longnose Gar

Bowfin

Holosteans have more advanced jaws than the chondrosteans. The posterior end of the maxilla is free, which allows it to swing forward, stretching the fold of skin. Instead of snapping the mouth shut, the fish produces a powerful sucton. Jaws are shorter and better supported and the scales tend to lose their shiny ganoid covering. From the Jurassic onwards, the holosteans dominated the world oceans, but, they became rare in the Cretaceous and are now largely extinct.

TELEOSTEI

The numbers of teleost species far exceed those of any other fish group, as 96% of living fishes are teleosts. They are the most successful fish group since their radiation in the Cretaceous. Teleosts have been found to survive in freezing Antarctic waters, in hot springs (up to 44 oC), in alkaline lakes, in acid streams, in the deep sea and in shallow rivers.

By the end of the Cretaceous, teleosts had become the dominant fishes in both the oceans and in freshwater habitats. Teleosts are characterized by a fully movable maxilla and premaxilla (which form the biting surface of the upper jaw); the movable upper jaw makes it possible for teleosts to protrude their jaws when opening the mouth. Teleosts are also distinguished by having fully homocercal (symmetrical) tails.

Teleosts include eels, catfish, tarpon, tuna, halibut, flounder, trout, cod, herring, salmon, and many other fishes.


Back to Subgroups page