We occasionally find and upload fossils. They have ecological significance for our region. When I uploaded some foam oysters, they were marked as casual because there was no particular policy for handling them.
When I recently uploaded an ammonite, it had the identification field of fossil added with an extinct tag auto-included, which is amazing. I must have missed the fix but am excited to use it going forward.
The family Gryphaeidae has extant species, so the “[extinct]” label won’t show up next to the name as it does for Ammonitida. Another user manually added the “Fossil: yes” observation field to your Ammonite observation. You can do this yourself for any of your other observations. You should also mark “no” for “recent evidence of an organism” in the DQA for any fossil observations.
I think iNaturalist is meant to be used for living extant and recently extinct lifeforms, not those that went extinct long enough ago to become fossils.
Fossils are not encouraged (and I think it’s fair to say they would be actively discouraged in very large numbers) but they are permitted. And fun. I got my first ammonite this year…