Wadi Al-Hitan is a very important fossil site that firmly establishes the fossil record of whale evolution from land mammals, one of Darwin's major assertions in The Origin of Species. The wadi hosts skeletons of families of archaic whales in their original geological and geographic setting of the shallow nutrient-rich bay of an early sea of some 30-40 million years ago, in what is now central Egypt.

There is no other place in the world yielding archaic whale fossils of such quality in such abundance and concentration -- over 400 cetacean skeletons have been discovered, the most important finds coming between 1985-1995. Many of the sirenians and cetaceans are preserved as virtually complete articulated skeletons which, uniquely, preserve reduced hind limbs, making them intermediate between earlier land mammals and later modern whales.