Tibetan paradise handed to ancient apes on a plateau, Chinese scientists believe

A tropical paradise that existed more than six million years ago on the Tibetan Plateau may have provided a final shelter for a common ancestor of humans and apes, a new study claims.

The theory follows the discovery of a well-preserved hominoid skull by an international team of anthropologists working at the southeast tip of the plateau in Yunan's Zhaotong Basin.

The skull, unearthed in 2013, puzzled researchers when tests dated it to 6.2 million years ago - long after the extinction of ancient hominoids elsewhere in the world about 9 million years ago.

It is widely believed that a change in the global climate that brought about very dry and cold conditions across much of the planet led to the extinction of less adaptive hominoids and the appearance of more modern apes and early humans.

But the new study posits that the southeast of the plateau was one of a few places spared from this change, providing a last refuge for ancient hominoids that lasted many years after they had died out in other parts of the world.

Led by professor Guo Zhengtang at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, the researchers used the latest microscopic scanning techniques to examine sediment samples from the fossil discovery site.

These revealed the quantity and mixture of pollen fossils in unprecedented detail, enabling the scientists to reconstruct a picture of the climate and vegetation at the time.

The environmental reconstruction showed that the last ancient hominoids lived in a cosy climate with rich biodiversity, and they were rarely thirsty due to an abundance of lakes and wetlands.

"During the time the hominoid lived, evergreen broad-leaved forests with evergreen Quercus were predominant, while grasses including Poaceae began to expand [while] conifers decreased, indicating a warm climate," they reported in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

The air was humid, too, with a "significant presence of aquatic pollen … suggesting the occurrence of [lakes] or swampy environments".

Compared to other regions in the world, such as Europe and Africa, where forests had largely disappeared due to coldness and drought, the Tibetan shelter preserved a much more favourable environment for the hominoids, the researchers said.

The special climate might owe very much to the rise of the Tibetan Plateau. Guo and colleagues speculated that the elevation of the landscape - caused by a tectonic collision between the Indian and Eurasian plates - might have created a barrier against the monsoon from the Indian Ocean.

But the shelter did not last long, at least in ancient terms.

From five million years ago, the vegetation began changing to coniferous forest, "indicating cooler and drier conditions", they reported.

The new climate, similar to the present day, was no longer suited to the ancient hominoids and led to their extinction.