- ARMOURED FISHES AND FISHES WITH ARMS
- CLASS PLACODERMI
The placoderms were armour-plated jawed fishes appearing
in Silurian about 420 mya and dominating the seas, rivers and
lakes until becoming extinct at the end of the Devonian. They
included some of the most bizarre vertebrates that ever lived,
such as the antiarchs, characterised by external bone-covered
arms, and the huge dinichthyids, the first creatures ever to
reach gigantic sizes of 8 m or more. The most successful groups
of placoderms were bothrolepidoids and asterolepoids that flourished
in Mid and Late Devonian worldwide.
Today placoderms are an important group for solving many geological
problems. They are useful as index fossils for giving age determinations
for Devonian sediments, and some groups have distinct biogeographic
ranges that suggest the positions of certain continents in past
geological times.
Summary by Dr. Irwin Haydock of the book entitled The Rise
of Fishes, 500 million years of evolution, by John A. Long, Johns
Hopkins University Press, 1995. (See Chapter 5)
If you would like to learn more about the evolution of fishes,
we highly recommend Long's book. It's excellent !! It's loaded
information that is well written and easy to understand.
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