Dinosaurs are earlier land animals.
I searched around on the internet before my previous post, and found to my surprise that there is indeed a debate on where birds come from...
http://www.animalplanet.com.au/birds/origins/index.shtml
http://www.nature.com/nature/journal/v279/n5710/abs/279234a0.html
(the nature abstract 27 years old, but was the only "semi-official" thing I could find)
The thing is though: people are debating where the bird "branched off" from dinos, or dino ancestors.
Taking a simplified dino-family tree:
http://www.cr.nps.gov/museum/exhibits/dino/graphics/familytree_small.gif
The discussion focusses on the place of the 'bird family line' in a family tree like this (some people place the branching-off-point before the beginning of this tree).
Everything I've read though, places the branching off point firmly in the territory of land animals. One theory seems to be that birds came from crocodiles, and you
could argue that crocodiles are marine animals, but in that theory, you would still have "true" land animals before you would have "true" birds.
Still, you're right that there is still a lot of fossil evidence to uncover, so the theories could still change around...
...but I don't know of any paleontologist who is searching for a fish-bird transitional.