In the Western Interior Seaway, where part of the Arctic Ocean had extended down North America, life flourished in the warm, shallow waters. Rising sea levels had created countless submerged islands, covered with a diverse array of marine creatures. Corals, sponges, and clams adorned the rocky surfaces, while schools of colorful fish swam in the clear blue water. But amidst all the bustling life, there was one spot that stood out. A large, bare rock jutted out of the water, devoid of any signs of life. Beyond it, the ocean dropped off into the deep sea, home to some of the most dangerous predators in the world.

One of these predators was the Mosasaurus, a mosasaur that ruled the seas during its time. It was over twice the size of a Tyrannosaurus and weighed over 15 tonnes. With its double-hinged jaws and flexible skull filled with four types of specialized teeth, it was a fearsome hunter, feared by all creatures in the Western Interior Seaway. But today, the Mosasaurus wasn't out for a hunt. Instead, it had come to the barren rock to be cleaned. The giant lizard rolled its massive body onto the rock, allowing the smaller fish and cleaner shrimps to pick off scraps of food from its teeth and scales. As they worked, the Mosasaurus shed its old skin, revealing a striking shade of red on its face and back, a sign that it was the mating season. The other inhabitants of the reef quickly realized that the Mosasaurus was not there to harm them. Instead, they joined in on the cleaning, using their specialized skills to remove the old skin and make the giant lizard look its best for the upcoming mating season. Among these creatures were the ferocious X-Fish, known for their powerful jaws, and the crow-toothed Squalicorax, a fierce predator. But even they knew better than to mess with the Mosasaurus during this time. As the giant lizard rolled around on the rock, the smaller creatures continued their work, cleaning even its belly.