many tropical marine animals, paving the way for entirely new species espe-
cially adapted to the cold.THE AGE OF FISH
The Devonian has been popularly named the “age of fish.” The widespread
distribution of primitive fish fossils throughout the world suggests a long ver-
tebrate record early in the Paleozoic.The fossil record reveals so many and var-
ied kinds of fish that paleontologists have a difficult time classifying them all.
Every major class of fish alive today had ancestors in the Devonian. However,
not all Devonian fish species continued to the present, having gone extinct in
the intervening time.
The rise of fish in the Devonian seas contributed to the decline of their
less mobile invertebrate competitors. This culminated in an extinction that
eliminated many tropical marine groups at the end of the period.When a mass
extinction occurs, those individuals that evolve into a better adaptive form areFigure 91Marine fauna
and flora of the middle
Devonian.
(Courtesy Field Museum of
Natural History)
Historical Geology