The spiny sharks became extinct at the Permian–Triassic extinction event; the conodonts became extinct at the Triassic–Jurassic extinction event.
The Cretaceous–Paleogene extinction event, and the present day Holocene extinction, have also affected fish variety and fish stocks.
The colonisation of new niches resulted in diversification of body plans and sometimes an increase in size.
They have been tentatively assigned to Agnatha by Janvier.
A third possible agnathid from the same region is Haikouella.
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.
These were followed by indisputable fossil vertebrates in the form of heavily armoured fishes discovered in rocks from the Ordovician Period 500–430 Ma.