Looking for sci fi/fantasy emphasis on creatures

[Pat]

Second Grass - awesome exploration of an alien ecosystem.

The world of Spatterjay in The Skinner by Neal Asher has one of the most bat-crap crazy ecosystems I've come across.

[CBRetriever]

Dogs of War by Adrian Tchaikovsky

[Carro]

Third vote for Grass

Add on Julie E. Czerneda with her trilogy starting with Survival. The main character is a migration biologist and this is set maybe a couple of centuries hence and her home base is this wonderful wilderness reserve on the NW seaboard of the US and she and her research team live in these brilliant floating pods just off the coast, to minimise their impact on the environment. Does students so very well.

[Ian]

On the Fantasy side, you might take a look at Patricia A. McKillip, beginning with the early The Forgotten Beasts of Eld (which was sometime marketed as juvenile/Young Adult, if memory serves). Her numerous more recent books usually have odd environments and creatures, but none immediately stand out in my mind for this in particular (and I am not up to date with her books anyway) -- with the exception of the magic-saturated forest in Alphabet of Thorn