Why are desert animals small?

Desert animals are small creatures because they have bodies that can adapt to the heat and dig into the earth to live in a burrow, as many desert animals do. Large animals cannot survive there.

For example, an elephant wouldn't be able to survive in the desert because: there just wouldn't be enough food for him to survive; he needs plenty of water to clean himself and to drink; some animals just aren't adjusted to the heat(although an elephant possibly could stand the heat,I wouldn't know).

But not all desert animals are small, the camel and the vulture are large animals, and it's mainly because the camel has two humps that store water to travel in the desert, and it has been living in the desert for thousands of years; while the vulture feeds of the spoiled carcasses of perished animals.