Entalognathus carries an ammonite trophy

Entalognathus is an ancient fish that lived around 419 million years ago. It's the first animal that has jaw bones that would later (in evolution) turn into faces. For reference: the fish is palm-sized.

There's a bit of speculative interpretation liberty that I allowed myself: teeth were never part of the found fossils. So, a large chunk of the fish's anatomy is up to our imagination and seeing parallels with similar fossilized critters.