This kind of criticism might be meaningless to many of you who're reading my comment, but I just like to say few(one) things that I noticed as illogical or as flaws in the nature - that is, encountering such living things in the wild.
I've read myriad of mangas regardless of its genre, of course, except those ones for girls(I am man), and I should say this, "Cage of Eden" is flawed for the part that the animals in this manga are not well performed. For example, as a generally accepted knowledge, we all should know that carnivores especially that of felidae in the jungle do not just appear right front of its prey, rather, they camouflage first and attacks second. But in this book, I noticed a saber-tooth cat just walks down the hill out of nowhere and screams for nothing then attacks(ch.2, pg.18-28). What a nonsense behavior. Another example, when an ambulocetus attacks(ch.11-12). Not only ambulocetus but all swimming creatures in the sea should move really fast that no human can ever stand up against especially in the case when a human was hunted to feed under sea, and the bone should also be crashed when it was bit. However neither happens in the scene.
Despite it is a mere manga, if it has as such degree as of this seriousness, I expect to see some reasonable logic based on the facts, and I would expect some increase in tension too. I will be enjoying more seeing a scene on the perspective of animal hiding like Steven Spieldberg's which will eventually create better suspension than a spotlight for nothing. Although, I praise for the author's effort, I think he/she must study harder for the subject beforehand if and only if he wishes to be the top of his game and not trick the audience intentionally or unintentionally.