Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Devonian
Contents
Overview
Life in the Devonian Seas
Terrestrial Habitats Conquered
The Devonian Extinction
and Tectonics during the Devonian
Evidence
Leaf and wood of Archaeopteris.
learn more
sample
Placoderm
Ammonite
Shark
Brachiopods
Trilobites
Centipede
Lobe-finned fish
Amphibian skull
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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Terrestrial Habitats Conquered
The Devonian was the time during which life truly conquered land. At the start of the period, terrestrial life was restricted to the narrow margin along the water’s edge. The first land plants had already evolved but still required a moist environment to reproduce. By the middle of the Devonian, the first shrub- and tree-like plants had appeared, some of which reached heights of five meters or more. By the Late Devonian, the first true trees and forests had evolved. This change is marked by the arrival of the genus Archaeopteris, whose species lived on nearly all Devonian landmasses. Like modern forms, these trees had extensive root systems, broad leaves, and specialized vascular systems that facilitated the flow of water and nutrients against the pull of gravity. All of these features helped plants colonize drier areas, which expanded life’s terrestrial habitat. Broad leaves provided shade and moderated temperature and humidity levels, whereas advanced root systems assisted production of the first soils (pedogenesis) by encouraging weathering of the land. These early forest habitats had important ecological effects on all other ecosystems. Gymnosperms appeared at the very end of the Devonian. These were the first plants to bear seeds, which allowed them to move farther into drier environments.

Following these plants, various arthropod groups also evolved terrestrial species, a development made possible by this new food source. Poorly known early arthropods included arachnids and flightless insects. Around 360 million years ago, after invertebrates had been on land for approximately 80 million years, the first tetrapods (“four feet”) appear in the fossil record. These early tetrapods evolved from lobe-finned fish at the very end of the Devonian and were ultimately ancestral to amphibians, reptiles, and mammals. Devonian tetrapods such as Ichthyostega and Acanthostega retained gills and many-fingered feet as adults, and probably were still aquatic. Fully terrestrial tetrapods did not appear until the Carboniferous.




Overview | Life in the Devonian Seas | Terrestrial Habitats Conquered
The Devonian Extinction | Climate and Tectonics during the Devonian



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