Oh I know that you aren't saying it was animals. Just some in the past maybe to make the convocation look less icky or whatever would always go for the it was plants and animals angle. It is hard to tell if the 1st two sacrifices had any kind of role they played (post acting as fuel). They did seem to dislike Fandaniel trying to assert control over them though. So they might had more to do than be in limbo. I also understand that they could evolve into people or just Zodiark fodder. Yet we know if they weren't people it'd take a bit for them to evolve enough into plant/animal people. Just look at the Ixal they used to be able to fly, but over five thousand years their arm feathers shrunk dramatically making them loose that ability.
I got that impression from shade Hythlodaeus and if Emet's convocation memory stone is about the new life Zodiark popped out then to me both hint that what came out wasn't what they were expecting. Course another problem that I don't think anyone has brought up before is we don't know a quantity for the new life. I know in the long run it wouldn't matter. But if said life wasn't meant to be more than just give the planet a kick start and was even as big as the amount of the 2nd sacrifice then the only reason to me at least to cultivate them is due to their thinness in aether. Which I mean why didn't Zodiark make em chunky? After all he should have been able to do so.
For me it comes down to A) they didn't make em chunky cause that's not how creations/familiars normally were made or B ) they for whatever reason couldn't pop out chunky aether bodies. Even after being allowed to rewrite the laws of the star. If B then one can assume there's a problem that doesn't allow for that. If A then they needed to (and obviously didn't get time to do so) stop thinking that new life that they make needs to be creation thin.