Tentaculites oswegoensis is a small animal of unknown origin that is often classified with molluscs or even as marine worms with a hard body. The genus Tentaculites was named in 1820 by von Schlotheim. This particular species was named in the late 1960s and is known from the Upper Ordovician rocks of the Maquoketa Group

Maquoketa Group

The Maquoketa Group is an assemblage of several geologic formations. It is Upper Ordovician in age and named for the Maquoketa River in Iowa. It exists in Missouri, Wisconsin, Iowa, Illinois, and Indiana. It is equivalent to the all but the basal formations of the Cincinnati Group in Ohio. ...

. It ranged from Oswego, IL (Kendall County) to possibly Kankakee River State Park

Kankakee River State Park

Kankakee River State Park is an Illinois state park on primarily in Kankakee and Will Counties, Illinois, United States. Originally, of land was donated by Ethel Sturges Dummer for the creation of the state park in 1938. Another was donated by Commonwealth Edison in 1956, and again donated more...

 (KRSP) in Will County, Illinois. At KRSP it appears in the basal Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 of the Kankakee Formation but has not been found in the underlying Ordovician rocks.

This particular species is approximately 0.75 to 1.25 inches in length. In Oswego, Illinois

Oswego, Illinois

Oswego is a village in Kendall County, Illinois, United States. As of the 2010 census, the village population was 30,355. Its population has more than doubled since the 2000 census count of 13,326...

 it is found mostly in clusters at Waubonsie Creek in the Basal Brainard Formation, just west of the railroad tracks. This entire class of animal became extinct at the end of the Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

and leaves no known descendants or related species.