Chondrostei

Stellate sturgeon (Acipenser stellatus )

• Worldwide

The Knorpelganoiden ( Chondrostei = " Knorpelknöchler " ) are primitive bony fishes ( Osteichthyes ) and form a sub- class of the ray-finned fishes ( Actinopterygii ). Their names they have from their cartilaginous skeleton, the little ossified, and the Ganoidschuppen that cover their skin partially or completely. Because of the construction of their pair of fins they are ( as " Palaeopterygii " ) compared with all other Strahlenflossern or Neopterygii. The sturgeon species ( Acipenseriformes ) are the only extant fish order, which is ranked among the Knorpelganoiden. In addition, have been and are in more conservative classifications still found many extinct groups of fish in the Knorpelganoiden.

Fish with cartilaginous skeleton and fossil Ganoidschuppenbedeckung are detectable from the Middle Devonian. They were the dominant group of fish bones from the Carboniferous to the end of the Triassic.

Features

Characteristic of which must be an Chondrostei animals the skull structure ( the upper jaw directed not directly on the neurocranium ), possession of an injection hole ( in most cases), the Ganoidschuppen, a heterocerke tail fin with Ganoid keel scales ( Fulcren ) at the top and the dense arrangement of the fin rays. The Interoperculare (an element of the gill cover ) is missing.

Conventional system

The monophyly of the Chondrostei in its old composition, as well as the lower taxa is controversial. The American ichthyologist Joseph S. Nelson notes in his standard work on fish systematics Fishes of the World, following orders in the Knorpelganoiden:

• Cheirolepidiformes †
• Guildayichthyiformes †
• Palaeonisciformes †
• Tarrasiiformes †
• Phanerorhynchiformes †
• Saurichthyiformes †
• Sturgeons ( Acipenseriformes )
• Ptycholepiformes †
• Pholidopleuriformes †
• Perleidiformes †
• Luganoiiformes †

In this composition, however, the Knorpelganoiden are a paraphyletic group, as they do not include all descendants of the most recent common ancestor.

Phylogenetic systematics

The following cladogram from a current palaeontological textbook the Knorpelganoiden are largely resolved and only the Birgeriidae remain as extinct sister group of the sturgeon species in addition to those within the monophyletic now Knorpelganoiden

Cheirolepidiformes †

Flössler ( Polypteriformes )

Guildayichthyiformes †

Mimiidae †

Stegotrachelidae †

Ptycholepiformes †

Amblypteridae †

Redfieldiidae †

Amphicentridae †

Dorypteridae †

Birgeriidae †

Sturgeons ( Acipenseriformes )

Palaeonisciformes †

Saurichthyiformes †

Pholidopleuriformes †

Perleidiformes †

Peltopleuriformes †

Neuflosser ( Neopterygii )