Didymograptus Murchisoni Small
''Didymograptus'' is an extinct genus of graptolites with four rows of cups. They lived during the Middle Ordovician, to Late Ordovician.''Didymograptus''
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Distribution

Fossils of ''Didymograptus'' have been found in Argentina, Australia, Bolivia, Canada (Northwest Territories, Quebec, Yukon, Newfoundland and Labrador), Chile, China, Colombia (

Middle Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The Ordovician, named after the Welsh 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 North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), 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 earlier Cambrian Pe ...
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