The fossils date back to the Silurian period, an important era for life on earth from 443 million years ago to 419 million years ago. Scientists believe our backboned ancestors, who were still swimming around on a watery planet, may have started evolving teeth and jaws around this time.

This let the fish hunt for prey instead of “grubbing around" as bottom feeders, filtering out food from the muck. It also sparked a series of other changes in their anatomy, including different kinds of fins, said Philip Donoghue, a University of Bristol paleontologist and an author on one of the studies.