There are lots of fossil observations, and even some projects, but most curators don’t really try to fit them into the tree. There’s enough other work to be doing that’s higher priority. Vertebrates especially will be hard, but you can still post casual observations.
Here’s some other relevant threads:
https://forum.inaturalist.org/t/identifying-fossils/11271
https://forum.inaturalist.org/t/dinosaur-footprints-fossils/4605
https://forum.inaturalist.org/t/fossils-in-rocks/5670