''Isograptus'' is an extinct genus of

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

s from the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

References

* Dinosaurs to Dodos: An Encyclopedia of Extinct Animals by Don Lessem and Jan Sovak Graptolite genera Paleozoic life of British Columbia Paleozoic life of Newfoundland and Labrador Paleozoic life of the Northwest Territories Paleozoic life of Yukon {{paleo-invertebrate-stub