You know what the debate over how dangerous trees are for protobirds reminds me of? Back when I was learning about whale evolution, I used to think "but wouldn't water be really dangerous for those early stages of amphibious proto-cetacean life?" (there's crocs, sharks, hungry fish, etc)
Not "etc.". There were crocs, there were sharks, but I don't know of any other big marine predators from the Paleo- or early Eocene.