- You may be looking for their reptilian successors.
The mammalian Betrushians were a highly advanced race in a variety of fields.
One of their creations was a type of organic catalyst which was able to test for biological viability of an organism and which would destroy any which were unsuitable. They were also able to create an ring of satellites which inhibited the catalyst and trapped it on the planet.
Millions of years ago, the Betrushians had an advanced civilisation. Unfortunately, their attempts to create a catalyst that could test for inadequate species was a failure and the catalyst lead to the extinctions of their species. Before this, the Betrushians were able to create the rings of Betrushia which trapped the catalyst on the planet and were able to leave a Polygon with the history of the experiment.