Wadi Al-Hitan (Valley of the Whales), is a protected area of some 20,015 ha in the Western Desert of Egypt. Fossil whales were first discovered here in 1905 and, since then, some 379 have been discovered, dating from the Eocene period, 56 to 34 million years ago. These whales cover an evolutionary period of 4 million years, from when the valley was beneath the Tethys Sea. Many of these fossils reveal that, during this period, ancient whales were in the process of losing their hind limbs, and making the final transition from land-based to purely sea-based creatures.