Stegouros was discovered in 2018 and formally described and named in 2021. Its skeleton was remarkably complete and included bony osteoderms, as well as its unique tail fully articulated.
Two other ankylosaurs were determined to be related to Stegouros – Kunbarrasaurus and Antarctopelta. Though their tails are not known, they may have had similar structures like Stegouros. They form a group called the parankylosaurs, which diverged from other ankylosaurs in the Early Cretaceous Period, and continued to thrive until the Late Cretaceous (Stegouros lived about 75 million years ago).
After the parankylosaurs diverged into a separate group, the remaining branch was known as Euankylosauria, which included Nodosaurids (which had no tail clubs, like Sauropelta), and Ankylosaurids (which had tail clubs, like Ankylosaurus).