Giant rhinos are among the largest land mammals that have ever lived on earth. Researchers have now discovered a new species of giants in northwest China: Paraceratherium linxiaense was around seven meters tall, had a long neck and, at 24 tons, weighed about as much as four elephants. The anatomical features of the new species provide information about relationships with other giant rhinos. Accordingly, P. linxiaense was closely related to a giant rhinoceros species from Pakistan. This suggests that the prehistoric giants once crossed Tibet before the area became a highland.
Giant rhinos lived in the open forest landscapes of Asia from around 47 million years ago to around 23 million years ago, especially in China, Pakistan, Kazakhstan and Mongolia. Individual fossil fragments have also been found in Eastern Europe, Anatolia and the Caucasus. The relationship between the various species and how they spread was not yet clear.
Giants 26.5 million years ago
A team led by Tao Deng from the Chinese Academy of Sciences in Beijing has now discovered a new species of giant rhinoceros that is helping to reconstruct the family tree of the giant land mammals. “We have found a completely preserved skull with an associated lower jaw and a cervical vertebra that belong to a new species of Paraceratherium,” the researchers report. In addition, they discovered the vertebral bones of another individual. Deng and his colleagues named the new species Paraceratherium linxiaense after it was found in the Linxia Basin in Gansu Province in northwest China. The site is on the northeastern edge of the Tibetan highlands and contains fossils from the late Oligocene. The researchers dated the bones of the giant rhinoceros to an age of around 26.5 million years.
“Paraceratherium linxiaense has characteristics that are typical of the genus, including a huge body size, a long intermaxillary bone and separate parietal bones,” describe Deng and his colleagues. Like all giant rhinos, P. linxiaense – unlike today’s rhinos – did not have a horn. “The new species differs from previously known giant rhinos, among other things, in a deeper nasal cavity,” the authors say. In addition, the cervical vertebrae show further adaptations to particularly large body sizes and a long, flexible neck. The skull is slender with a short nasal trunk.
Spread through Tibet
Using the anatomical features of the giant rhinoceros, the researchers analyzed how it was related to other members of the genus. Accordingly, the newly discovered species is likely derived from P. bugtiense, another species of giant rhinoceros that was common in western Pakistan. This is indicated in particular by the shape of the lower jaw, which is similar to that of P. bugtiense, but is larger and more specialized. P. linxiaense’s neck was also probably more flexible than that of its Pakistani ancestors.
By comparing various fossil finds of giant rhinos, Deng and his colleagues reconstructed how the giant mammals spread across Asia. The first ancestors spread in the early Oligocene from Mongolia to Kazakhstan. After further evolutionary differentiations, which led to the species P. bugtiense, the giant rhinos expanded to South Asia. “In the late Oligocene, tropical climates allowed the giant rhinoceros to return north to Central Asia,” the researchers write. Here the species split into two new species, one of which returned to western Kazakhstan and the other, P. linxiaense, established itself in the Linxia Basin region.
The prehistoric giants had to cross Tibet in this way. “That means that the Tibetan region was not yet a high plateau at that time,” the authors say. This is also indicated by other evidence such as fish and plant fossils, which suggest that the region was less than 2000 meters above sea level almost 30 million years ago. “The results suggest that Tibet did not yet exist as a highland in the late Oligocene and therefore did not represent a barrier to the migration of large land mammals,” the researchers conclude.
Source: Tao Deng (Chinese Academy of Sciences, Beijing) et al., Communications Biology, doi: 10.1038 / s42003-021-02170-6