Definitions for ordovicianˌɔr dəˈvɪʃ ən
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Ordovician, Ordovician period(noun)
from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds
Of a geologic period within the Paleozoic era; comprises lower, middle and upper epochs from about 488 to 443 million years ago.
The Ordovician period.
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 485.4 ± 1.9 to 443.4 ± 1.5 million years ago. It follows the Cambrian Period and is followed by the Silurian Period. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods respectively. Lapworth, recognizing that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, realized that they should be placed in a period of their own. While recognition of the distinct Ordovician Period was slow in the United Kingdom, other areas of the world accepted it quickly. It received international sanction in 1960, when it was adopted as an official period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it did in the Cambrian, although the end of the period was marked by a significant mass extinction. Invertebrates, namely mollusks and arthropods, dominated the oceans. Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. Life had yet to diversify on land.
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