Devonian period
This period is part of thePaleozoic era. |
Cambrian |
Ordovician |
Silurian |
Devonian |
Carboniferous |
Permian |
| Table of contents |
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2 Devonian dating 3 Devonian subdivisions 4 Devonian palaeogeography 5 Devonian fauna |
Devonian naming
The Devonian is named for England's Devonshire area where Devonian outcrops are common. The Devonian follows the Silurian period and precedes the Mississippian subperiod of the Carboniferous.
Devonian dating
The Devonian is a geologic period that extends from about 360 to 408.5 million years before the present. As with most older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the end of the period is uncertain by 5-15 million years.
Devonian subdivisions
The Devonian is usually broken into Lower, Middle, and Upper subdivisions. The Faunal stages from youngest to oldest are:
- Famennian/Chautauquan/Canadaway/Conneaut/Conneautan/Conewango/Conewangan (Upper)
- Frasnian/Senecan/Sonyea/Sonyean/West Falls (Upper)
- Cazenovia/Cazenovian (Middle)
- Givetian/Erian/Senecan/Tioughniogan/Tioughnioga/Taghanic/Taghanican/Genesee/Geneseean (Middle)
- Eifelian/Southwood (Middle)
- Helderberg (Lower)
- Emsian/Sawkill/Deer Park (Lower)
- Pragian/Siegenian (Lower)
- Lochkovian/Gedinnian (Lower)
Devonian palaeogeography
The southern continents remained tied together into the Supercontinent Gondwana. In equatorial regions, North America and Europe formed a continent. The remainder of modern Eurasia lay in the Northern Hemisphere.
During this time period, the subcontinent of Euramerica was home to all of the new things that the Devonian brought. Sea levels were high world wide. Much of the land lay under underneath shallow seas, where tropical reef organisms lived. A huge, deep ocean covered the rest of the planet
The Devonian was called the “greenhouse age.” Widespread reefs indicated that the climate was mild and warm, as well as generally dry.
Devonian fauna
Sea levels in the Devonian were generally high. Fish were abundant and diverse. The first sharks appeared early in the period. Bony fish, many of substantial size appeared shortly thereafter. Small land plants appeared early in the period. By the end of the period forests of primitive plants existed. Both vertebrates and arthropods were solidly established on the land. Marine faunas continued to be dominated by bryozoa, brachiopods and corals. Trilobites were still fairly common, but less diverse than in earlier periods.
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