Paraceratherium: The Largest Land Mammal That Ever Lived

Paraceratherium was a giant hornless relative of the rhinoceros that lived in Asia between about 34 and 23 million years ago, during the Oligocene Epoch. Standing up to about 5 metres at the shoulder and weighing an estimated 15 to 20 tonnes, it is usually regarded as the largest land mammal that ever lived. Known also by the older names Baluchitherium and Indricotherium, it was a long-necked browser that fed on trees much as giraffes do today.

A giant of Oligocene Asia

The Oligocene was a time of global cooling after the warm Eocene. In parts of Asia, forests gave way to more open woodlands and drier landscapes, and many mammal groups evolved larger body sizes.

Paraceratherium belonged to the paraceratheriids, a group of hornless rhinocerotoids that also includes smaller, earlier forms. Its fossils have been found across a vast area, including Pakistan, Kazakhstan, Mongolia and China, with related remains reported from as far west as Turkey and the Balkans.

Discovery and confusing names

The first fossils were described in 1911 by the British palaeontologist Clive Forster-Cooper, who named Paraceratherium bugtiense from teeth and bones found in the Bugti Hills of Balochistan, then part of British India and now in Pakistan. Two years later he named Baluchitherium from further remains in the same region.

In 1916 the Russian palaeontologist Aleksei Borissiak named Indricotherium from fossils collected in the Turgai region of Kazakhstan, after the Indrik, a mythical beast of Russian folklore. In 1922 Walter Granger of the American Museum of Natural History found a huge skull in Mongolia during the Central Asiatic Expeditions led by Roy Chapman Andrews, the same expeditions known for the Gobi dinosaur eggs. Henry Fairfield Osborn named it Baluchitherium grangeri in 1923.

For decades these names were used side by side. In 1989 the researchers Spencer Lucas and Jay Sobus argued that they belonged to one genus, and Paraceratherium, as the oldest name, took priority. Some palaeontologists still keep Indricotherium separate, so the classification is not fully settled.

How big was it?

No complete skeleton has ever been found, so size estimates are built from partial skeletons, comparisons with living rhinos and calculations based on limb bones. This has produced a wide spread of figures over the past century.

Early estimates reached 30 tonnes, but these are now seen as exaggerated. Most modern studies suggest a weight of roughly 15 to 20 tonnes for the largest individuals, a shoulder height of about 4.5 to 5 metres and a body length of about 7 to 8 metres. The skull alone was about 1.3 metres long.

Its claim to the title of largest land mammal is not unchallenged. Some estimates for extinct elephants, especially Palaeoloxodon namadicus of India, are similar or higher, but those are based on very fragmentary remains.

How it lived

Paraceratherium had long, pillar-like legs with three toes on each foot and a long neck. With its head raised it could probably reach leaves some 7 metres above the ground.

Its upper front teeth formed a pair of downward-pointing tusks, and the shape of the skull suggests a mobile upper lip or a short proboscis. These would have helped it strip leaves and twigs from trees. Like elephants, it probably needed huge quantities of food and travelled long distances in search of it.

Large adults would have had few predators, though young animals were probably vulnerable to large crocodiles and carnivorous mammals. By analogy with modern rhinos and elephants, they likely grew slowly and raised few young.

Recent finds

New fossils continue to refine the picture. In 2021 a team led by Deng Tao of the Chinese Academy of Sciences described Paraceratherium linxiaense from a well-preserved skull and jaw found in Gansu Province, China. Their analysis suggested that the giant rhinos moved between Central Asia and the Indian subcontinent through corridors that were open during the Oligocene.

Extinction

Paraceratherium disappeared around the end of the Oligocene or early Miocene, roughly 23 million years ago. The exact causes are unknown.

Commonly proposed factors include climate change that reduced the forests it fed on and the arrival in Asia of proboscideans, the group that includes elephants, from Africa. Elephant relatives can push over and strip trees, which may have transformed habitats and competed with the giant rhinos for food. Much later, other large herbivores such as the woolly mammoth would face their own climate-driven pressures. Smaller rhinos continued to thrive, including the barrel-bodied forms preserved at the Ashfall Fossil Beds in Nebraska.

Timeline

• c. 34 million years ago: Early giant rhinos appear in Asia at the start of the Oligocene.
• 1911: Clive Forster-Cooper names Paraceratherium bugtiense from the Bugti Hills.
• 1913: Forster-Cooper names Baluchitherium.
• 1916: Aleksei Borissiak names Indricotherium from Kazakhstan.
• 1922: Walter Granger finds a giant skull in Mongolia.
• 1923: Henry Fairfield Osborn names Baluchitherium grangeri.
• 1989: Lucas and Sobus unite the names under Paraceratherium.
• 2021: Paraceratherium linxiaense is described from Gansu, China.

Why it matters

Paraceratherium shows how large a land mammal can become and helps scientists study the physical limits of body size. Its tangled naming history also illustrates how palaeontology revises its classifications as fossils from different countries are compared.