Like, I’m aware of there being exceptions like Penguins, Ostriches, and Bats. But in general, why is there such a distinct land/air split between mammals and birds? Why don’t mammals share the ground with ecosystems of plant- and meat-eating walking birds? Why didn’t we get birds that evolved to slither like snakes, or tunnel like rodents? Why isn’t it (land+sky) all just mammals, where we’d have parrot- and vulture-like bats that don’t lay eggs? If we started the simulation again, might things like this evolve?
There are a lot of types of creatures figuring and fighting out their ecosystems.
And the land we say is just the surface of the Earth. There are insects, ameba, bacteria they may not be birds or mammals but they are also part of like and ecosystem and it boils down to everyone contributing to the cycle.
This may not be the answer but something to ponder upon as it helps you to visualize life.
Bees and vultures are so so cool as well