Silurian
The Silurian (/sɪˈljʊəriːən, saɪ-/ sih-LURE-ee-ən, sy-) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
| Silurian | |||||||||||||
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Map of Earth during the early Silurian, c. 440 Ma | |||||||||||||
| Chronology | |||||||||||||
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| Etymology | |||||||||||||
| Name formality | Formal | ||||||||||||
| Synonym(s) | Gotlandian | ||||||||||||
| Usage information | |||||||||||||
| Celestial body | Earth | ||||||||||||
| Regional usage | Global (ICS) | ||||||||||||
| Time scale(s) used | ICS Time Scale | ||||||||||||
| Definition | |||||||||||||
| Chronological unit | Period | ||||||||||||
| Stratigraphic unit | System | ||||||||||||
| First proposed by | Roderick Murchison, 1835 | ||||||||||||
| Time span formality | Formal | ||||||||||||
| Lower boundary definition | FAD of the Graptolite Akidograptus ascensus | ||||||||||||
| Lower boundary GSSP | Dob's Linn, Moffat, United Kingdom 55.4400°N 3.2700°W | ||||||||||||
| Lower GSSP ratified | 1984 | ||||||||||||
| Upper boundary definition | FAD of the Graptolite Monograptus uniformis | ||||||||||||
| Upper boundary GSSP | Klonk, Czech Republic 49.8550°N 13.7920°E | ||||||||||||
| Upper GSSP ratified | 1972 | ||||||||||||
| Atmospheric and climatic data | |||||||||||||
| Sea level above present day | Around 180 m, with short-term negative excursions | ||||||||||||
One important event in this period was the initial establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution: vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized.
A significant evolutionary milestone during the Silurian was the diversification of jawed fish and bony fish.