When I tell you that flounder are pretty cool fish, you might think that I mean that they taste good or you might be thinking of Ariel’s only real friend, the yellow-and-blue Flounder:
Well, you would be wrong on both counts. What I mean is that real-life flounder are a type of flatfish, and as such they have a really interesting feature: extreme asymmetry, in that both of their eyes are on the same side of their body. This is because they spend most of their time on the sea floor, and so their predators are generally going to come from above (so it pays off to have two eyes on the incoming-predator side). Here’s a picture of an actual flounder:
Well, the reason I’m telling you all of this is because there has been a recent discovery about how both eyes came to be on the same side of the flatfish. Scientist have been wondering about this for some time now, and now there is fossil evidence that the eyes slowly migrated. A transitional-stage fossil flatfish has been discovered, and it has one eye in a normal position but the other eye is towards the top of the other side of its body. Transitional fossils like these make pretty compelling arguments for the path that evolution took to get us where we are now.