An international team of scientists led by Dr. Tao Deng of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, has discovered a 4.6 million-year-old species of three-toed horse in southwestern Tibet.

In their paper, published in the Proceedings of the National Academy of Science, the scientists report the discovery of a well-preserved skeleton of three-toed horse, named Hipparion zandaense.

The fossilized specimen of H. zandaense was collected in August 2009 from the Zanda Basin, southwestern Tibet.

The Tibetan Plateau is the youngest and highest plateau on the planet. Its elevation reaches one-third of the height of the troposphere, with profound dynamic and thermal effects on atmospheric circulation and climate. The uplift of the plateau was an important factor of global climate change during the late Cenozoic and strongly influenced the development of the Asian monsoon system. There have been hot debates about the history and process of Tibetan Plateau uplift.

Because both morphology and attachment impressions on fossilized bones can reflect muscular and ligamentous situations, they can provide evidence for the type of locomotion that extinct animals used when they lived. The skeleton of H. zandaense preserved all limb bones, pelvis, and partial vertebrae, which provide an opportunity to reconstruct its locomotive function.

Morphological features indicate that H. zandaense was a cursorial horse that lived in alpine steppe habitats. The horse had the ability to run fast and stand persistently, which is beneficial only on open habitats, because close forests would encumber running.

Because this open landscape would be situated above the timberline on the steep southern margin of the Tibetan Plateau, the elevation of the Zanda Basin about 4.6 million years ago was estimated to be about 4 km above sea level using an adjustment to the temperature in the middle Pliocene as well as comparison with modern vegetation vertical zones.

The scientists conclude that the southwestern Tibet achieved the present-day elevation in the mid-Pliocene.