Bilaterally symmetrical animals
TELEOSTOMES
Teleostomes developed a hard flap to protect their gills. Teleostomes use oxygen for respiration, but also used it for buoyancy when it was wholly aquatic. The oxygen was stored in a gas bladder which has evolved into lungs in non aquatic teleostomes.
Teleostomi contains all amphibians, reptiles, birds and mammals.
Teleostomi can be separated into euteleostomi which make up the very large majority of the world's current vertebrates, and the extinct acanthodians.
Acanthodians are also called spiny sharks because they were shark like animals which were covered in scales of some form.
Acanthodians had thick and rigid spines which acted as supports for their fins.
The acanthodians are believed to be the first type of teleostome which existed possibly from around 440 million years ago.
Euteleostomes are made up of bony skeletons as opposed to cartilage skeletons and most of today's fish can be categorised as euteleostomes, but certainly not all.
Humans are euteleostomes.
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Bony vertebrates |
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ACANTHODII Extinct spiny sharks |
