Clonograptus

Graptolites, like this Amplexograptus from the Ordovician near Caney Springs, Tennessee are good zone fossils. A zone fossil must have a short time span but a common animal of the time. Graptolites became extinct at the end of the Devonian.

Clonograptus is a genus of graptolites. Groups of these animals were connected by stalklike structures to a central region. Species of Clonograptus are zone fossils, that help us estimate a precise age of Ordovician rocks.[1]

References

  1. ↑ http://www.britannica.com/EBchecked/topic/122072/Clonograptus
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