The fossils of Wadi Al-Hitan dating back to 50 million years show the youngest archaeocetes, in the last stages of evolution from land animals to a marine existence. They already display the typical streamlined body form of modern whales, whilst retaining certain primitive aspects of skull and tooth structure, as well as hind legs. Many of the whale skeletons are in good condition as they have been well preserved in the rock formations. Semi-complete skeletons are found in the valley and in some cases, even stomach contents are preserved. Fossil of other early animals such as those of sharks, crocodiles, sawfish, turtles and rays found at Wadi al-Hitan makes it possible to reconstruct the surrounding environmental and ecological conditions of the time.
There is considerable evidence which indicates that the basin of Wadi Hitan was submerged in water some 40 to 50 million years ago. At that time, the so-called Tethys Sea reached far south of the existing Mediterranean. The Tethys Sea is assumed to have retreated north and over the years deposited thick sediments of sandstone and limestone visible in rock formations in Wadi Hitan.
Geological studies have been carried out in the area since the 1800's, and the first skeletons were found around 1830 but were never collected due to the difficult accessibility to the site at that time. At first, it was thought to be a huge marine reptile. It was only later in 1902, that the species were identified as whales. For the next 80 years they attracted relatively little interest, largely due to the difficulty of reaching the area. In the 1980s interest in the site resumed as four wheel drive vehicles became more readily available.
Wadi Al-Hitan, now a Unesco World Heritage site, is visited by only 1,000 people each year.
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