Most of animals don't leave any fossils, especially without skeleton. Special conditions are required for fossilification [1].

1. https://www.americangeosciences.org/education/k5geosource/co...

Many upon many. The _vast_ majority of species are left out, and for ones that do have fossils the _vast_ majority of individuals are left out.

Something getting fossilized is basically a miracle, and us finding it is another on top.

A relatively recent discovery points to macroscopic multicellular life as early as 2.1B years ago (1), right after the Great Oxidization Event. We only have fossils of a single specie. Given the complexity of the specimens, it's unlikely to have been the only specie in existence. The rest of the biota is probably lost to time.

The fossil record for Ediacarian biota (pre-Cambrian age) is also very sparse. It's only after the evolution of endo/exoskeletons that we start to get proper fossil records

(1) - https://en.wikipedia.org/wiki/Francevillian_biota

Absolutely. Also consider that a vast portion of the Earth's crust has been recycled into the mantle over the millenia.

The vast majority of extinct animal species is like that. Fossilization is an incredibly rare event.

The good news is that all modern fossils leave plenty of signatures in the form of legislation