Answer:
One major trend in animal evolution has been the gradual increase in the ratio of brain size to body mass. Birds of the late Cenozoic have larger ratios than cretaceous avians. This same general principle holds true for mammals, of course. I'm not so certain the relation carries over to reptiles (diapsids), turtles (anapsids), or fish.
Of course, there are cephalopods, insects, and hoary hosts of other animals. I'm not as familiar with evolutionary trends in marine species.