Anyone see the resemblance with 'Natural Selection'?
There is a 2006 horror novel by David Freedman, "Natural Selection" which posits intelligent manta rays (the novel calls them DemonRays) that evolve via natural selection. Among their other abilities, they can fly, not just glide, and can stay out of water for extended periods of time. Oh, and we're on their menu!
As soon as I saw the previews, I thought of this novel. It was a pretty creepy read, certainly good enough to stay with me these seven years!