Monster life starting from picking up materials

When you see a male Rathalos flying across the sky, you cannot conclude that it is a male Rathalos, because it is possible that before you see it, it is a rare Silver Rathalos.
When you suspect it was a Silver Rathalos before, it could have been a Spinosaurus even longer ago.
When you learn from other people that it was a Spinosaurus long ago, you still cannot conclude that it is a Spinosaurus, because it is possible that it was a Nergigantes before others saw it.
You can almost be sure that it is a flying dragon, but you still cannot assert that it is a flying dragon, because underground where you can't see it, it may be an old mountain dragon.
So what is it?
In the beginning, it was a hairy spider.