Osteichthyes : Overview

The Osteichthyes or bony fish are one of the two major clades of fish, and hence of vertebrates, the other being the Chondrichthyes or sharks. Durong the mid Paleozoic (presumably the middle to late Silurian), there was an explosive radiation of vertebrates, following the adaptive opportunities made possible by jaws and teeth and the more efficient ways of food gathering these made possible. First the original gnathostomes gave rise to placoderms and acanthodians, along with a number of smaller, little known groups. Then the Acanthodii gave rise to both the Chondrichthyes and Osteichthyes. Finally, Osteichthyes or bony fish gave rise to Actinopterygii or "ray-finned fish" and Sarcopterygii or lobe-finned fish. These latter included lungfish, coelocanth and various Paleozoic groups, from which the first amphibians (or tetrapods, to use the cladistic term, amphibians being a paraphyletic group are not considered taxonomically valid, although the present author disagrees with such an approach). It would however be a mistake to think that once the first still fish-like amphibians had appeared, fish no longer evolved, and indeed, became irrelevant. An anthropocentric perspective of that sort, according to which all life is a chain of ascent to man, is still based on 19th and 19th century ideas of a great chain of being, whereas evolution is better thought of as a branching tree. So, at the same time amphibians were evolving into reptiles, and reptile sinto birds and mammals (to say nothing of the innumerable forms and variations of amphibians, reptiles, birds, and mammals that this evolutionary path took), sharks and bony fish were evolving in all sorts of amazing ways too (as were invertebrates, plants, and microorganisms...).

The very vigour of that evolutionary process means that the poor cladogram node that is Osteichthyes (shown in bold in the dendrogram at the upper left) only gets brief coverage, because by its very success it quickly gave rise to ray fina nd lobe finned fish, with the original stem or ancestral bony fish quickly (by geological standards of many millions of years that is) becoming extinct. For now, this unit is one of the shorter on Palaeos, a quick discussion of Clade Osteichthyes, before passing to the various descendent lineages. MAK111027

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