Evolution of fish

Devonian fish

The evolution of fish began about 530 million years ago during the Cambrian explosion. One of the earliest jawless fish include Haikouichthys, a craniate. The conodonts were another Agnatha. The earliest jawed vertebrates developed during the late Ordovician period.

During the Devonian period, a great increase in fish variety occurred, especially among the ostracoderms and placoderms, and also among the lobe-finned fish and early sharks, which meant that this was the age of fishes.

Agnatha

The mouth of a lamprey

The Agnatha (meaning "no jaws") is a superclass of fish in the phylum Chordata, subphylum Vertebrata. Agnatha comes from the Greek. The first armoured agnathans were the ostracoderms, precursors to the bony fish and hence to the tetrapods.

Conodonts

The conodonts are an extinct group of agnathans that looked like eels. They appeared 520 ma and died 200 ma. One of them is Promissum.

Chondrichthyes

Main article: Chondrichthyes

The Chondrichthyes, consisting of sharks, rays and chimaeras, appeared by about 395 million years ago, in the middle Devonian.

Extinct cartilaginous fishes

• Helicoprion - a fish famous for its tooth whorls
• Goodrichthys
• Megalodon

Living fossils

Materpiscis

Main article: Living fossil

• Frilled shark
• Gars
• Australian lungfish
• Protanguilla palau
• Bowfin
• Coelacanths
• Bichir

Bony fish

Actinopterygii

Main article: Actinopterygii

Actinopterygii

Actinopterygii is the class of ray-finned fish. Actinopterygians are the largest class of vertebrates.

Sarcopterygii

Main article: Sarcopterygii

Lobe-finned fishes, class Sarcopterygii, are mostly extinct bony fishes. They lived a very long time ago. Most of them died already, while few, such as the coelacanths, have survived.

The first tetrapodomorphs, which included the rhizodonts, had the same general anatomy as the lungfish, who were their closest kin, but they appear not to have left their water habitat until the late Devonian epoch (385 - 359 Ma), with the first appearance of tetrapods.

Devonian fish

Placodermi

Main article: Placoderm

The placoderms were a class of armoured prehistoric fish.

Dunkleosteus

Main article: Dunkleosteus

Nerepisacanthus

Dunkleosteus was a giant arthrodire that lived during the Devonian period.

Materpiscis

Main article: Materpiscis

Materpiscis was a ptyctodontid fish from the Late Devonian.

Related pages

• Ichthyolith
• Walking fish

References

1. Lecointre, G; Le Guyader, H (2007). The Tree of Life: A Phylogenetic Classification. Harvard University Press Reference Library.
2. Haines, Tim; Chambers, Paul (2005). The Complete Guide to Prehistoric Life. Firefly Books.

Other websites

• Evolution of fish on English Wikipedia