Holostei

Common gar ( Lepisosteus osseus )

The Knochenganoiden ( Holostei [ from Greek " holosteos " = very boney ] ), also called bone melting scaler, are a group of primitive bony fish that are found only eight species in North and Central America as well as in Cuba today, in the Mesozoic ( Mesozoic ) but were used in great shape diversity. The modern species include up to three meters long pikes ( Lepisosteidae ), the externally see the pike -like and live as a shock predators in rivers and lakes of North America and Central America, and the bowfin ( Amia calva ), also called mud fish, eastern from the North America.

Features

Knochenganoide are large to medium-sized fish that have an elongated, round in cross-section body in general. With Kyphosichthys only one really hochrückige genus is known ( Dapedium is now regarded by many scientists as a core group of representatives Teleostei ). The body is scaly with Ganoidschuppen, a primitive Schuppenart, consisting of a bony surface that is covered with a nacreous layer of shiny Ganoin, where the Cosmi layer but has already been lost. The internal skeleton is completely ossified. Vertebral bodies are formed. The caudal fin is externally almost symmetrical, the caudal skeleton inside but clearly heterocercal. In the shoulder girdle, the clavicle is lost. The intestine has a rest on a spiral fold ( four turns in Lepisosteus ). The swim bladder dorsally lying can be used in the extant species to breathe atmospheric air, as it was in the extinct forms, remains unknown. The number of fin rays is usually low and corresponds to the unpaired fins of the number of fins carrier.

The Knochenganoiden are best to diagnose over her jaw mechanism. The Palaeonisciformes the mouth was long with trailing far corners of the mouth. The Knochenganoiden it is shorter, the maxilla is shortened and has lost its rear extension. Contact with the Vorkiemendeckel and Ectopterygoid was lost, as was the contact with the bone below the orbit. At the upper edge of the maxilla is the Supramaxillare often yet another bone added. The Vorkiemendeckel has been reduced to a crescent- shaped front edge of the gill cover and the newly added Interoperculum closes the gap in the throat region, which is formed in the forward movement of the jaw. The orbit is behind and below but still surrounded by bone circumorbitalen the complete bone coverage of the sides of the head was lost. This region is more or less at the Holostei "naked" or covered with various bone plates. Hyomandibular, Os quadratum and Epiptpterygoid are reinforced as a carrier of the jaw apparatus and an additional bone, the symplectic and hyomandibular quadratum Os can join.

History

The term Holostei was for the first time by Johannes Peter Müller, a German marine biologist and comparative anatomist, used to Polypterus and Lepisosteus to unite. Amia, who was previously a member of the Clupeidae ( herrings ), was added by the German -Swiss scientist Carl Vogt, after he had examined his heart. Polypterus was expelled in 1861 by Thomas Henry Huxley again from the group. In the following, the group consisted of more than 100 years and was used to summarize recent Mesozoic and primitive bony fish of a particular stage of development. The limits were fluent in both the original Knorpelganoiden ( Chondrostei ) as well as to the more developed genuine bony fish ( Teleostei ). The fish of the transition zone between Chondrostei and Holostei were called Subholostei. It existed long suspected that this is an artificial polyphyletic group at the Holostei.

Throughout the 1970s and 1980s continued after comparing the skull bone outside more and more by the view that the Amiiformes, the order to which the bowfin belongs and the Teleostei must have had a common ancestor. The common taxon of Amiiformes and the Teleostei was called Halecostomi. The Holostei thus became an invalid taxon.

More recently, however, show both molecular studies as well as more accurate and reinterpreted comparisons of the morphology that the Amiiformes are more closely related to the Lepisosteiformes than with the Teleostei.

In 2010, the Holostei have therefore been revalidated.

Outer systematics

Knorpelganoide ( Chondrostei )

Knochenganoide ( Holostei )

Pachycormiformes †

True bony fish ( Teleostei ).

Inside systematics

Semionotiformes †

Kyphosichthys †

Billfish behaved ( Lepisosteiformes )

Parasemionotiformes †

Ionoscopiformes †

Caturidae †

Amiidae

Within the Knochenganoiden, two separate groups differ, the Ginglymodi with the gars and some extinct groups, as well as the Halecomorphi whose representatives up on the mud fish are all extinct.

• Knochenganoiden ( Holostei ) wrestled loose taxon Ginglymodi Order billfish behaved ( Lepisosteiformes )
• Order Semionotiformes †
• Incertae sedis Kyphosichthys †

• Order Parasemionotiformes †
• Order Ionoscopiformes †
• Order Amiiformes Family Amiidae
• Family Caturidae †
• Family Liodesmidae †
• Family Sinamiidae †