(Ice Age, image source: animatedviews.com)
Tsamma Melons, a relative to watermelons you would find the the grocery store, grow wild in the Kalahari desert is South Africa. Storing large amounts of water and resistant to drought, they are a good water source as well as food source for animals living in the region, including humans and kori bustards.
If you grow watermelons in a garden in North America you might end up sharing them with some wild neighbours. Raccoons, deer, coyotes, and especially crows are all animals that might eat a watermelon if they found one.
Despite being at the top of the food chain, coyotes also will eat watermelon. At night a coyote might sneak into a garden where it will break open a watermelon and eat the flesh right down to the rind.
The coyote's distinctive destruction to the fruit contrasts with the method which raccoons and deer eat watermelons. They will dig or puncture a hole through the skin to get to the inside.
Pumpkins, too, are a reason for wildlife visitors in some gardens. Rabbits only eat the leaves (not the fruit itself), nibbling at the tips, similar to it's habitual sampling of leafy greens.
Using their digging abilities, mice and moles get to the seeds inside pumpkins by digging a tunnel through the bottom and into the middle. Squirrels, and chipmunks may also dig through a pumpkin in pursuit of the delicious seeds that await inside, sometimes even being found digging through pumpkins left of porches. Unlike the others, woodchucks eat the actual flesh of the fruit.
Bauer, Mary. What wild Animals eat Watermelons in a Garden?
Kane, Dan. Tsamma Melons: Watermelon's Wild Cousins.