Paraceratherium, the “Giant Hornless Rhinoceros,” could very well have been the largest land mammal of all time. However, we do not have a complete specimen so we cannot yet know its true size. Paraceratherium transouralicum is our most complete species, and is estimated to have been around 15-16 feet at the shoulder, about 24.3 feet long, and weighing between 33,000 and 44,000 pounds, slightly taller than a giraffe and longer than an elephant. The only other contender for largest land mammal is Palaeoloxodon namadicus, the Asian straight-tusked elephant, but we have even less material there.
Paraceratherium lived in the Oligocene, all across Eurasia, in habitats varying from arid desert to subtropical forest. Like elephants and sauropods, it was a high browser, and due to its size it would have had very few predators. The only animal capable of taking on an adult would have been the 33-36 foot long crocodile, Astorgosuchus.