You ever think about Ediacaran biota?
Dickinsonia costata
They lived 550 million years ago! And nobody knows what these are! They might be animals, but we're not sure!
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@vaporeon_ this is neat. is there a reason we assume this was something that was once alive and not, say, an impression left by a weird rock?
@wallhackio For a different Ediacaran lifeform, they found what looks like traces of it moving around, look at the picture here: https://en.wikipedia.org/wiki/Yorgia#Trace_fossils
But ultimately, we can't know! We can't observe it, we only have fossils! I wish I had a time machine... I want to see the Ediacaran biota...
@wallhackio Good question! I don't know... I'm not a paleontologist, I'm just a nerd who likes old stuff... If I had to guess, it's because we found multiple of these in different sizes, various stages of growth
Wikipedia has this photo of a fossil of one with a chunk of it missing, and that really looks like a formerly-living thing to me and not a rock: https://en.wikipedia.org/wiki/Dickinsonia
They also say:
And judging by the abstract of the article, I really do think that it's about the different stages of growth and also the regeneration, rocks can't do that
But unfortunately, I can't get a PDF of the linked article