While cephalopods large and small spread throughout the Ordovician oceans, hunting, filtering, or scavenging (or perhaps all three), a rather tangential and unassuming lineage called vertebrates produced the first proper fish. They had fins and tails and gills; they even had skulls—but no jaws. They slurped up whatever food didn’t need biting or chewing and were therefore almost certainly no threat to cephalopods. Then, in the subsequent Silurian period, these odd bony creatures evolved something truly dangerous. Jaws were just as effective as beaks for catching and eating prey.
