Today’s Tibetan Plateau reaches into the sky—a craggy expanse of high-altitude steppe butting up against the towering Himalaya. But 26.5 million years ago, parts of this region were dotted with humid woodlands, giving refuge to another kind of skyscraper: one of the biggest mammals to ever walk on land.
The newfound creature, unveiled today in the scientific journal Communications Biology, is an extinct cousin of today’s rhinoceros called Paraceratherium linxiaense. The colossal animal would have weighed up to 24 tons, four times heavier than today’s African elephants, and its skull alone was around a metre long.
It’s the latest known species in a group of giant, hornless rhinos that lived across Central Asia from roughly 50 million years ago until 23 million years ago. P. linxiaense and its kin are all famous for their huge sizes. The average adult is thought to have stood more than 16 feet tall at the shoulder, with a nearly seven-foot-long neck topped by a massive skull. Today’s giraffes are between 14 and 19 feet tall, head and all.
The giant rhinos “would have been able to eat flowers at the third or fourth floor of a building,” says National Geographic Explorer Pierre-Olivier Antoine, a rhino palaeontologist at France’s University of Montpellier who reviewed the new study.
P. linxiaense was among the last of these giants, called paraceratheres, living about 26.5 million years ago. Thanks to their age and location, the new fossils, including a complete skull, a mandible, and three vertebrae, are helping fill out the paracerathere family tree, shedding new light on where these towering rhinos evolved and how they spread across the present-day continent of Asia.
A prehistoric giant
Paraceratherium fossils are rare and often fragmentary, making it hard to chart the genus’s evolution and spread. The group’s longtime home appears to have been Central Asia, but the first species of Paraceratherium ever found, P. bugtiense, lived in what is now western Pakistan. How exactly did this giant rhino get all the way to the Indian subcontinent?
Researchers led by Tao Deng, a mammal palaeontologist at China’s Institute of Vertebrate Palaeontology and Paleaoanthropology in Beijing, have now found that the new species P. linxiaense was closely related to the Pakistani P. bugtiense, and that hints at the Pakistani rhino’s origins.
The new fossils hail from the brown sandstones of central China’s Linxia Basin. Here, sediment layers up to 1.2 miles thick tell the story of the last 30 million years of Earth’s history, peppered with fossils from the ancient creatures that once lived in the region.
In the 1950s, farmers in the area claimed to have found “dragon bones.” For a time, these remains were sold to medical companies and used as ingredients in traditional Chinese medicines. By the 1980s, palaeontologists recognised that the region preserved scientifically valuable fossils from the late Oligocene epoch, the time period 23 to 28 million years ago.
Ever since, palaeontologists with the Institute of Vertebrate Palaeontology and Paleoanthropology have studied the Linxia Basin’s rocks and the rich array of fossils they contain.
In May 2015, Deng and his colleagues came across a rare find near the village of Wangjiachuan: the complete skull and mandible of a giant rhinoceros, as well as three vertebrae from another individual. When the researchers saw the 26.5 million-year-old bones—including the 3.8-foot-long skull—their preservation and size came as “a great surprise to us,” Deng says.
Based on its similarities to the giant rhino from Pakistan, the new findings suggest that giant rhinos moved freely across thousands of miles between Central Asia and the Indian subcontinent between 30 and 35 million years ago. Tropical conditions at the time “allowed the giant rhino to return northward to Central Asia, implying that the Tibetan region was still not uplifted as a high-elevation plateau,” Deng writes in an email—an idea that is backed up by geologic evidence suggesting the area still had some low-lying parts until about 25 million years ago.
Mysteries of the giant rhino
Antoine, the French palaeontologist, says the new study helps reveal geographic patterns that governed the giant rhinos’ movements across ancient Earth. A catalog of giant rhino fossils in the new research suggests that the animals never crossed from Asia into Europe through the Ural Mountains, for example, indicating the mountain range may have acted as a barrier.
The research may also help explain how the huge creatures arrived in what’s now Turkey, where fossils of the rhinos have also been found. According to Antoine, fossils that have not yet been described in a scientific paper suggest that after giant rhinos arrived in present-day Pakistan, they made their way into Turkey across what is now Afghanistan and Iran.