I don't know why they call this Silverwing, #4 - it really has nothing to do with the Silverwing series.
My 6 year old LOVES the evolutionary aspect of these pre-bats (made up, of course) of 65 million years ago, plus other creatures whose evolutions we witness (and the demise of the dinos). I gave it 5 stars both because it was rather well written and an unusual concept, but mainly b/c it's the only evolutionary fiction of prehistoric animals I've ever come across and it completely down L's alley.
It wasn't as dark as Silverwing. Just the typical nature show type predator-prey scenes, but also a morality aspect.