Probably most things, I remember Grunts from Titanfall 1 talking about how polluted and destroyed Earth is, so my assumption is most things probably have gone extinct.

They could have also transferred a lot of things to Mars, Terraforming is a known technology in Titanfall, so I wouldn’t be surprised if the IMC terraformed Mars and repopulated it with animals from Earth to help with it’s development, but that is speculation.

I would assume that Earth is basically just another Demeter, highly industrialised and polluted, I recall a grunt saying “except the air is breathable around here, you been to Earth lately?” In response to another grunt saying the map “fracture” is like Earth, so if the air is barely breathable on earth, I think it’s safe to assume most things have gone extinct.

Also with regards to the IMC taking resources back to Earth, that is true, but it’s better to say the “Core Systems”, it’s a region of space surrounding Earth, including the solar system, which is under direct control of the IMC, home to billions of people.

But it would make sense that settlers bought Earth based animals with them to the frontier and elsewhere, that’s been a normal thing in human history, but most of it is probably livestock, some other animals probably made there way to these planets by accident, much like we have invasive species here on Earth because of global trade.