What it is
A predatory ray-finned fish from rocks about 280 million years old in the Parnaíba Basin of northeastern Brazil. It hunted in rivers and lakes. All that is known of it is one skull, about as long as a finger.
Holes for fangs
Each jaw had three rows of teeth, and the inner rows carried large curved fangs. When the jaws closed, the lower fangs slid into a line of holes on the inside of the upper jaw. Without those holes, the jaws could not have shut all the way. The front of the jaw has no holes, because the front fangs were smaller.
Not tooth sockets
Scientists scanned the skull with X-rays and rebuilt the jaws on a computer to watch them close. The holes do not line up with the upper teeth, so they were not sockets for new teeth. No other fish of its age is known to fit its fangs this way.