Ancient Fish
The first vertebrates — from jawless armoured agnathans to lobe-finned tetrapod ancestors and giant pelagic hunters.
Overview
This hub spans the early history of fishes and their relatives — jawless armoured agnathans, the first jawed vertebrates (placoderms), spiny acanthodians, cartilaginous sharks, and the bony fishes, including the lobe-finned forms that gave rise to all land vertebrates.
Quick Facts
Key Characteristics
- •Earliest forms lacked jaws; gnathostomes evolved jaws from gill arches
- •Placoderms bore heavy bony head and trunk armour
- •Lobe-finned fishes (sarcopterygians) have fleshy, bone-supported fins — precursors of limbs
- •Lungfish and coelacanths are the nearest fish relatives of tetrapods
Fossil Record
Fish fossils range from micro-fish debris to spectacular complete skeletons: Miguasha (Canada), Old Red Sandstone (Scotland), Green River Formation (Wyoming), Solnhofen and Gogo Formation (Australia) preserve whole armoured and bony fishes, sometimes with soft tissue.
Global Distribution
Global, with Devonian 'Old Red Sandstone' faunas of Scotland, Canada and Russia, and Cenozoic lake and marine deposits worldwide.
Evolutionary & Scientific Importance
Fishes record the origin of jaws, the vertebrate invasion of land (Tiktaalik and its relatives), and the ancestry of every backboned animal. Devonian fish faunas are key to correlating early continental deposits.
Classification
Fishes are an informal assemblage of several distinct lineages, not a single class — grades like 'Agnatha' are paraphyletic.