Largest land mammal ever

Owing to limited fossil evidence, there are currently three contenders for the record of largest land mammal ever: Paraceratherium (a type of gigantic extinct rhino called an indricothere with giraffe-like long necks and tall, slender skeletons), the straight-tusked elephant Palaeoloxodon and Borson’s mastodon (Mammut borsoni). For decades, the title fell exclusively to the indricothere Paraceratherium, best represented by a partially reconstructed composite skeleton in the American Museum of Natural History in New York City, USA, said to measure 5.41 m (17 ft 9 in) tall at the shoulder and 11.27 m (37 ft 11.7 in) in total length, and weighing in at a whopping 34 tonnes (37.5 tons). However, this New York giant is, in fact, a chimera comprising of remains from several different individual animals, excavated in Mongolia in the 1920s during the Museum’s Central Asiatic Expeditions. More reliable estimates for the larger New York specimens suggest a shoulder height of 4.8 m (15 ft 9 in), and around 7.4 m (24 ft 3.3 in) in total length, calculated to weigh around 17 tonnes (18.7 tons).

In 1993, the partial skeleton of an even larger Paraceratherium was discovered in the Xinjiang region of north-west China. The Xinjiang Paraceratherium skull is 1.33 m (4 ft 4.4 in) long, making it the largest indricothere skull found. Together with preserved parts of the spine, the Xinjiang Paraceratherium was estimated to have been around 7.2 m (23 ft 7 in) long. Comparisons with modern rhino and horse skeletons produced an estimated weight of 18.5 tonnes (20.4 tons) for the Xinjiang Paraceratherium. By comparison, a modern African white rhino, the largest of the living rhinos, can achieve a body length of 3.77 m (12 ft 4.4 in) and weigh 3.6 tonnes (4 tons), standing up to 1.85 m (6 ft) at the shoulder.

A 2016 study suggested that the extinct straight-tusked elephant Palaeoloxodon, which lived some 700,000–50,000 years ago, surpassed Paraceratherium in size with weight up to 22 tonnes (24.3 tons) and shoulder height of 4.5 m (14 ft 9 in). Yet this estimate was only based on a fragmentary femur found in India, so is rather speculative. The more complete limb bones from another Indian Palaeoloxodon yield a more modest estimation at 13 tonnes (14.3 tons) and shoulder height of 4.35 m (14 ft 3 in). Intriguingly, these leg bones came from an elephant of late teenage/early adult age; a full-grown animal could thus easily have weighed over 15 tonnes (16.5 tons), with weight and height on par with more conservative estimates for the biggest indricotheres.

In 2007, the largest mastodon tusks ever found were excavated from Milia in northern Greece, at 5.02 m and 4.39 m (16 ft 5.6 in and 14 ft 4.8 in) long respectively. The remains came from a Borson’s mastodon (Mammut borsoni), which inhabited vast parts of Eurasia between 5 and 2.5 million years ago. Mastodon limb bones found at Milia in association with the enormous tusks indicate massive individuals weighing in the region of 15–16 tonnes (15.5–17.6 tons), with a shoulder height of around 4.1 m (13 ft 5 in).

Since the extinction of the dinosaurs (with the exception of birds) 66 million years ago, mammals evolved many truly spectacular and enormous forms, of which the biggest land animals today pale in comparison. Often, the magnificence of these bygone beasts are apparent even from their scanty partial fossil remains, but more reliable estimates of body size can only be attained through known relationships between skeletal measurements and body mass in modern animals, particularly those comparably built such as elephants, rhinos and camels. Different measurements of fossil remains (e.g., skull length or femoral circumference) produce different body size estimates; palaeontologists also dispute which specimens are referable to which fossil species, and the number of species of extinct giants that once existed.