According to now-outdated wisdom about the formation of the Solar System, there should be nothing this big this far beyond the plutinos
This includes a group of four dubbed Plutinos
because, like Pluto, their orbit has a special synchrony with that of Neptune.
These icy bodies belong to a group of Kuiper-belt residents called Plutinos
because like Pluto, they make two orbits about the sun in the time that Neptune makes three.