The new coral species Streptelasma rutkae and a cephalopod belonging to the genus Gorbyoceras occur in nearshore shallow-marine sandstone of the Whirlpool Formation in Hamilton, southern Ontario. They are the first macrofossils contributing to a modern understanding of the geologic age and correlation of this formation. Streptelasma rutkae most closely resembles a species that occurs widely in the Edgewood Biogeographic Province of the east-central United States, in rocks dating to the latest part of the Ordovician Period. Gorbyoceras is present in Late Ordovician rocks in the Cincinnati Arch region. Thus, the occurrences of Streptelasma rutkae and Gorbyoceras support other fossil and chemical data suggesting that the age of the Whirlpool Formation is latest Ordovician, rather than earliest Silurian as traditionally thought. They also indicate paleogeographic connections between the area where the Whirlpool Formation was deposited in Ontario and the Edgewood Biogeographic Province and Cincinnati Arch region in the east-central United States.

Solitary rugose corals assigned to Streptelasma rutkae n. sp. and an annulated orthoconic cephalopod identified as Gorbyoceras sp. occur in nearshore shallow-marine sandstone of the Whirlpool Formation in Hamilton, southern Ontario. They are the first macrofossils contributing to a modern understanding of the age and correlation of this stratigraphic unit. Streptelasma rutkae most closely resembles S. subregulare (Savage, 1913), which occurs widely in the Edgewood Province of the east-central United States, in strata considered latest Ordovician (Hirnantian). Gorbyoceras ranges into the latest Katian (latest Richmondian) in the Cincinnati Arch region. Thus, the occurrences of S. rutkae and Gorbyoceras sp. support other biostratigraphic and chemostratigraphic data suggesting that the Whirlpool Formation is latest Ordovician, rather than earliest Silurian as traditionally thought. They also indicate paleogeographic connections between the area of Whirlpool deposition in Ontario and the Edgewood Province and Cincinnati Arch region in the east-central United States