(410 to 360 mya)
Land is colonized by plants and animals.
Appearances include: insects; sharks; amphibians (tetrapods);
lung fishes and earliest seed plants.
Extensive radiation of fishes.
seas swarmed with many kinds of unique fish during Devonian
time. In fact, fishes were the only vertebrates on Earth until
the Upper Devonian. Because of the extensive radiation of fishes,
the Devonian is often called the age of fishes. Throughout the
Devonian while the ancient jawless fish and placoderms remained,
new more advanced forms were appearing. Devonian fish were some
of the first vertebrates to evolve, and can be grouped into
five classes: 1) agnatha or "jawless fish"; 2) spiny
fish; 3) Placoderms or "platedskins"; 4) Chondrichthyes
or otherwise known as sharks, and; 5) the bony fishes. Many
of the armored fish became extinct at the end of the Devonian,
and the lobe-finned fishes and lungfishes markedly declined.
The cartilaginous fish, sharks and rays were likely the last
group of fish to evolve.
earliest animals with backbones were the class known as Agnathas
that are most commonly called "jawless fish". Most
of these fish had "shell skins" and lived in rivers
and lakes from 510-350 million years ago. As scavengers, they
sucked in water containing food perticles through slots in their
first trees appeared in the Devonian, and had developed the
vascular system to grow to some 20 feet tall by the end of the
Devonian. Also appearing were the Lycopods (scale trees and
club mosses) that reproduced by means of spores; these went
on to thrive through the Carboniferous but met extinction by
the end of the Paleozoic.
Devonian seas were filled with brachiopods, and by tabulate
and rugose corals that built large bioherms, or reefs, in shallow
waters. In the Lower Devonian, ammonoids appeared, leaving large
limestone deposits from their shells. Bivalves, crinoid and
blastoid echinoderms, graptolites, and trilobites were all present,
though most groups of trilobites disappeared by the close of
major animal groups colonized the land. The first tetrapods,
or four legged land-living vertebrates, appeared during the
Devonian, as did the first terrestrial arthropods, including
wingless insects and the earliest arachnids.