''Ceraurus'' is a genus of cheirurid trilobite of the middle and, much more rarely, the upper

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. ...

. They are commonly found in strata of the lower

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five la ...

region. These trilobites have eleven thoracic segments, a very small

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is com ...

and long genal and pygidial spines. ''Ceraurus'' is quite common in the Ordovician of upstate

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

, south-central and south-eastern

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central C ...

, and the St. Lawrence Valley in Quebec, as well as in the

Canadian Arctic Northern Canada, colloquially the North or the Territories, is the vast northernmost region of Canada variously defined by geography and politics. Politically, the term refers to the three territories of Canada: Yukon, Northwest Territories and ...

. It and similar genera range in size from less than quarter an inch to well over five inches. Similar genera of trilobites occur in the Ordovician outcrops of the

Volkhov River The Volkhov (russian: Во́лхов) is a river in Novgorodsky and Chudovsky Districts of Novgorod Oblast and Kirishsky and Volkhovsky Districts of Leningrad Oblast in northwestern Russia. It connects Lake Ilmen and Lake Ladoga and forms par ...

, near St. Petersburg, Russia. The taxonomy of the genus is problematic, as the many variations of eye placement, decoration patterns of pustules, and spine length call the genus' defining characteristics into question. ''Ceraurus'' may, in fact, be at least four genera: ''Ceraurus''

sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...

, and the genera, ''Gabriceraurus'', ''Bufoceraurus'' and ''Leviceraurus''.

References

* Ludvigsen, Rolf, Fossils of Ontario: Part I: The Trilobites. Toronto: Royal Ontario Museum, 198

Cheiruridae Phacopida genera Extinct animals of North America Ordovician trilobites of North America Middle Ordovician first appearances Late Ordovician extinctions Bromide Formation Paleozoic life of Ontario Verulam Formation Paleozoic life of British Columbia Paleozoic life of the Northwest Territories Paleozoic life of Nunavut Paleozoic life of Quebec {{phacopida-stub