User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-2248808-20110826032448/@comment-1680839-20110906020611

There are many species of animals that are called "living fossils" because they have survived millions of years without significant evolution, therefore I would say that the modern green Rathian is rather a subspecies of the ancient Rathian. Also, about the question of Ancient Rathian out-competing modern Rathian, it could be that, while Ancient Rathian are immensely powerful, modern Rathians appear to be better at breeding (IMHO, if I'm a los, I'd rather score with a green ian than a scary dark purple one :P), and adaptations have allowed their offspring a better chance at survival than Ancient Rathian, which means that modern Rathian are actually out-competing Ancient Rathian by number.