Freshwater Fossil

[Gilby]

Found this fossil loose on a limestone shoreline on St. Joseph Island located at the north end of Lake Huron in Ontario, Canada. I am a civil engineer and have some experience with rocks but I’m fairly new to fossils. Any help identifying would be great!

[Thomas.Dodson]

Looks like an orthocone nautiloid from the Paleozoic. Some of our Canadian members might be familiar with the exact age of that bedrock offhand or you can find what it says on a Geologic Bedrock Map of the area as well.

[Rockwood]

I think it may be a siphumcle of a larger nautiloid. The feature which crosses the outline could be geologic, but I doubt it.

I think Ordovician would be a reasonable guess as to the age.

[PaleoOrdo]

5 hours ago, Thomas.Dodson said:

Looks like an orthocone nautiloid from the Paleozoic.

It might be an orthoconic nautiloid, maybe an endocerid in view of the rounded form of the apex. But it is difficult be certain since it is not preserved well and seems have some curve.

[Kane]

Much of St Joseph Island is Gull River Formation, early Ordovician in age. That being said, since it was found on the shoreline, it could be another formation, but will still be Ordovician in age. The rocks along the eastern shore usually come out white, whereas those along the bridge out of the island are grey and somewhat crumbly with fauna more a fit with Gull River Fm.