Subdivisions
Events of the Devonian Period -420 — – -415 — – -410 — – -405 — – -400 — – -395 — – -390 — – -385 — – -380 — – -375 — – -370 — – -365 — – -360 — – -355 — Silurian Lochkovian Pragian Emsian Eifelian Givetian Frasnian Famennian Carbon-iferous ← Rhynie chert ← Hangenberg event ← Kellwasser event(s) ← Widespread
shrubs & trees ← S. America
glaciation begins ← Hunsrück fauna
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Key events of the Devonian Period.
Axis scale: millions of years ago.
The Devonian Period is formally broken into Early, Middle and Late subdivisions. The rocks corresponding to these epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System.
The Early Devonian lasts from 419.2 ± 2.8 to 393.3 ± 2.5 and begins with the Lochkovian stage, which lasts until the Pragian. This spans from 410.8 ± 2.8 to 407.6 ± 2.5, and is followed by the Emsian, which lasts until the Middle Devonian begins, 393.3± 2.7 million years ago. The Middle Devonian comprises two subdivisions, the Eifelian giving way to the Givetian 387.7± 2.7 million years ago. During this time the armoured jawless ostracoderm fish were declining in diversity; the jawed fish were thriving and increasing in diversity in both the oceans and freshwater. The shallow, warm, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop essential characteristics such as well developed lungs, and the ability to crawl out of the water and onto the land for short periods of time.
Finally, the Late Devonian starts with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests were taking shape on land. The first tetrapods appear in the fossil record in the ensuing Famennian subdivision, the beginning and end of which are marked with extinction events. This lasted until the end of the Devonian, 358.9± 2.5 million years ago.
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