*** Welcome to piglix ***

Primitive fish

Fish
Fossil range: Mid Cambrian–Recent
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
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
Scientific classification
Kingdom: Animalia
Phylum: Chordata
(unranked) Craniata
Included groups
Jawless fish
Armoured fish
Spiny sharks
Cartilaginous fish
Bony fish
Ray-finned fish
Lobe-finned fish
Excluded groups
Tetrapods
External video
Evolution Of Jaws 1 of 5 Animal Planet
Evolution Of Jaws 2 of 5 Animal Planet
Evolution Of Jaws 3 of 5 Animal Planet
External video
Chordate Evolution and Bony Fish YouTube
External video
Pikaia gracilens animation
The Burgess Shale
External video
BothriolepisAnimal Planet
External video
DunkleosteusAnimal Planet
External video
The mother fishNature
External video
Tetrapod Evolution Animal Planet
1 2 3 4 5
Evolution fish with fingers Transitional fossilsYouTube
External video
EusthenopteronAnimal Planet
External video
IchthyostegaAnimal Planet
Pierce et al Vertebral Architecture
1
2 3 4 5YouTube

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).


...
Wikipedia

...