Spyroceras sp. is a genera that is known from the Ordovician period up through the Devonian period. that gives it an age range of 100 million years that the genus is recognized in the fossil record. It's doubtful that a single species lasted that long, but it does speak to the success of the genus. Below is an example of the genus that I found at the Deep Springs Rd. borrow pit in New York. It comes from the Windom shale member of the Moscow formation (middle Devonian, Givetian stage). It is easily recognized by the straight, orthoconic shell that has regularly spaced growth rings that are perpendicular to the rest of the shell. If there was enough detail on the impression I might be able to narrow down the species based on the presence of striae that can sometimes be seen between the growth rings but are parallel to the shell's growth.
Specimen #1
This is a 3-D fossil cast of the shell so it pops off and you can see both sides.
Specimen #2 - This may be a different species, perhaps
Spyroceras nuntium which is known for having more closely spaced annulations and coarser striae.
I found an example of
Spyroceras sp. in the Ordovician aged
Verulam formation here (scroll to the bottom of the post).
These specimens were found at a borrow pit on Deep Springs Road in Madison County, NY which exposes the Windom shale member of
the Moscow formation (middle Devonian in age, Givetian stage.)
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