Looga the 3rd was born. Today he and his friends were exploring looking for food. There was a lot of fresh decay around them that they enjoyed making use of. But his inside explorer wanted more.
He previously found a strange not decay. It was weird and smooth like no other, at least not like anything he would have known. He and his family is what we would call abominations, freaks of nature. Not that I would call him that to his face. The only reason they were able to survive was with supernatural powers. Loogas was super intuition. Using that he found something very smooth.
Now he and his friends decided to explore because of their boredom. Looga, Mooga, tooga, and fooga gathered. Mooga was a warmth breather, tooga could eat anything and fooga was a nobody, just really friendly. Or at least not known yet.
So they were exploring the place. Mooga using his breath or create light. It was really smooth. Unnaturally smooth. And following the hallway they came across a fellow abomonid. Only it was no longer living as their senses told them. As they continued down they came across a disturbing scene.
Many nonliving being scattered the hallway. Looga feeling something wrong told them to go back. The others not listening pushed on. To which they all perished or so looga thoughts as his instinct told him to run.
Little did he know that only fooga survived.
Going back to camp he told the others of the demise of the others and went to live his life fearfully never again exploring fearing the smooth dungeon. As loogas many offspring spread, they spread the word of the dungeon known for it's fatalities but might hold unknown treasures from societies long past.
As the radiation stabilized the monster were spread and many with different varieties and different abilities. Imitating what they found in what little nature was left as from the depths of the ocean new life was born that came to the surface. Restarting the cycle of life again.
Loogas descendants now made camp around major dungeons sending parties everynow and then. Some found small intact dungeons that they excavated. They found manuscripts, devices, and images that they began to covet and imitate. Eventually some even were able to fly, now becoming so distinct that different creatures were hardly able to recognize and communicate with each other. And with certain creatures limited intelligence it didn't even matter. They created an ecosystem themselves.
While the more intelligent types were finally able to desipher the manuscripts creating bases and warding off the monsters using their powers learning about 'humans' and 'superhumans' and also about monsters as were depicted in the oracles of the dungeons, the intelligent types also knew that the larger dungeobs held more knowledge than the smaller ones. However the larger ones were filled with monsters for whatever reason.