N any extinct Palaeozoic colonial animal of the class Graptolithina, usually regarded as related to either the hemichordates or the coelenterates: a common fossil, used to determine the age of sedimentary rocks 笔石
During the Ordovician, most life was in the sea, so it was sea creatures such as trilobites, brachiopods and graptolites that were drastically reduced in number.
在奥陶纪，大多数生命都生活在海洋里，所以海洋生物，例如三叶虫、腕足类动物与笔石动物的数量在此时急剧减少。
Between one edge of the three-foot-thick gray band and the other, some 80 percent of marine species died out, many of them the sorts of creatures, like graptolites, that no longer exist.
在约1米厚的灰色岩石带子的各个带层之间，约80%的海洋物种灭绝了，其中许多是生物物种，象笔石动物，再也不会在这个世界上存在了。
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