Strunius rolandi

Strunius rolandi from Wikipedia

Name: Strunius rolandi

When: Late Devonian Period, about 370 million years ago

Where: Numerous localities and Germany and Latvia

Claim to fame: The Devonian Period is called not called "the age of fishes" because the first fish lived then. Fish have been around much longer, but the diversification of fish accelerated in the Devonian. A huge part of this the explosion of the bony fish - Osteichthyes. Living bony fish fall into two great groups:

• Ray-finned fish - including most living bony fish
• Lobe-finned fish - common in early oceans, but rare today as fish - limited to coelacanths and lungfish. (Psst! Land vertebrates are lobe-finned fish whose ancestors left the water!)

So, what about Strunius? This little fish is fun because it gives us a snapshot of what lobe-finned fish looked like just barely after their split with ray-finned fish. Indeed, looking at its fins, you really can't tell that it's a lobe-fin, but there is a big hint in its skull: The skulls of primitive lobe-fins come in two parts - a front and rear part that articulate at a moveable joint. You can see how this functions to increase the strength of the bite in the living coelacanth Latimeria. Turns out that Strunius had this feature, too, allowing us to identify it as a very basal lobe-fin. But Strunius has its own special adaptation: Where its jaws come together at the front of the mouth, the teeth form a saw-blade-like symphyseal tooth whorl that it could extend and retract and that fit into a special socket in the roof of its mouth. This is easy to see in its big relatives like Onychodus. So, a tiny snapshot of the beginnings of lobe-fin evolution, but not a slouch!