One of my interests is speculative zoology, but I'm not interested about fauna of alien planets. I think it's a very good question that what animals will in the Earth in a few million years.
I wasn't see, but I read the 'After Man' and the Neocene Project, I offer these two.Have you seen the documentaries "The future is wild"? If not, I highly recommend to you.
In the 1980s there was a popular book speculating what the current biota of Earth might evolve into once humans go extinct. I remember whale-sized penguins were one of them. It was popular enough that there was a series of animatronics made for a traveling exhibition like the traveling dinosaur exhibits that go from zoo to zoo. The name of the book and the author elude me. I saw the animatronic show at the San Diego Wild Animal Park in 1991.
Have you seen the documentaries "The future is wild"? If not, I highly recommend to you.