[naasking]

How many introduced species are there as a percentage of all existing species? This seems like an important number to calculate the probability that we might have missed such an introduced species given the fossil record we have.

It could also be that introduced species are less likely to be found in the fossil record for whatever reason.

Then again, maybe we have found such a thing but haven't recognized it for what it is due to missing context.

[BuyMyBitcoins]

That’s a good point, and I don’t have an answer. In my mind I was thinking of more obvious examples, like camels being introduced to Australia. Or cichlids from Lake Victoria being introduced into isolated lakes in North America. The idea being that you would notice some very obvious out-of-place fossils.

I also assume that these species, often invasive, would outlast the civilizations that introduced them. So you could probably also infer some of this by looking at descendant populations.

[naasking]

We would naturally just assume that the same species appearing in different places just implied that those places were closer together in the past + migration. And so we have Pangaea before continental drift.

If we lacked progenitors of those species in some places, we would just call it a temporary gap in the fossil record, of which we have many.

We're pretty good at inventing explanations. Eventually these gaps might start looking conspicuous, but I'm not sure if we're at that point yet.

[melagonster]

but we have good prove of continental drift now. before we getting enough evidences, this theory just a joke.

[naasking]

You've missed the point, because these theories are basically compatible with the existing evidence, they just tell a different story.

[BuyMyBitcoins]

I suppose a counter example would be a species found on multiple continents but during a time when they weren’t joined together. But you’re right that a natural overlap due to past plate tectonics could lead to false negatives with what I’m suggesting.

[naasking]

Right, but how could we know that they weren't joined together? We don't have DNA evidence for a lot of history so we build narratives from morphological evidence. If we find the same or similar species in two different places, we would typically just create a narrative around one of two possibilities, a) these two places were closer together at one point, or b) there was some great exodus from a common origin driven by factors unknown. The former is something like Pangaea, the latter describes human exodus from Africa.

Eventually there might be enough separate lines of evidence to refute these possibilities, but no one aside from those on the fringe would entertain the possibility that this was evidence of an advanced culture without overwhelming evidence.

[inglor_cz]

"are there as a percentage of all existing species"

Percentage of total biomass is more interesting. The more (and bigger) bodies, the higher the likelihood of being fossilized.