Primitive fish
| Fish Fossil range: Mid Cambrian–Recent |
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 The Devonian period 419–359 Ma (Age of Fishes) saw the development of early sharks, armoured placoderms and various lobe-finned fishes including the tetrapod transitional species
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 Evolution Of Jaws 1 of 5 Animal Planet
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Evolution Of Jaws 2 of 5 Animal Planet
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Evolution Of Jaws 3 of 5 Animal Planet
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Chordate Evolution and Bony Fish YouTube
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Pikaia gracilens animation The Burgess Shale |
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Bothriolepis – Animal Planet
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Dunkleosteus – Animal Planet
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The mother fish – Nature
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Tetrapod Evolution Animal Planet 1 2 3 4 5 |
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Evolution fish with fingers Transitional fossils – YouTube
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Eusthenopteron – Animal Planet
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Ichthyostega – Animal Planet
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Pierce et al Vertebral Architecture 1 2 3 4 5 – YouTube |
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include Haikouichthys. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. Most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. Lamphreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans.
The first jawed vertebrates probably developed during the late Ordovician period. They are first represented in the fossil record from the Silurian by two groups of fish: the armoured fish known as placoderms, which evolved from the ostracoderms; and the Acanthodii (or spiny sharks). The jawed fish that are still extant in modern days also appeared in late Silurian: the Chondrichthyes (or cartilaginous fish) and the Osteichthyes (or bony fish). The bony fish evolved into two separate groups: the Actinopterygii (or ray-finned fish) and Sarcopterygii (which includes the lobe-finned fish).
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Wikipedia