Devastated by the zerg
Zz'gash is an inhospitable desert world seemingly located just outside the Koprulu sector. It has harsh weather. The dune runners were found on this world, and were adapted to survive its harsh conditions.
Prior to the Great War the zerg descended upon the planet, assimilating the planet's dune runners into the Swarm to become zerglings. Any other fauna the desolate planet may have featured would have been eradicated.