I think it’s a kind of mushroom.
Inkcaps of some sort, but hard to say which species, as the caps have deliquesced. Maybe Coprinus comatus.
It might be something else - Coprinopsis picacea is also a possibility.
NB: I’m sure you weren’t about to eat them anyway, but never do so on the basis of photo ID alone, especially on the internet.
Agreed. Outside of a few common species, inkcaps are notoriously hard to key out. You need fresh specimens and a microscope for many and since sometimes they will literally start breaking down the same day, it can be tricky even then. Can’t even tell you what family they are anymore because the whole group has recently turned out to be a paraphyletic mess - much to everyone’s surprise apparently deliquescing gills has evolved multiple times in highly disparate groups.
On the plus side the general descriptor of “inkcap” is super-easy to make :).