Indricotherium - The largest terrestrial mammal
Skull on display at the American Museum of History of Natural History, New York City
Reconstruction was part of the traveling Extreme Mammals exhibit, photo from when it was at the AMNH.
When: Eocene and Oligocene (~ 34 to 23 million years ago)
Where: Asia and Eastern Europe
What: Indricotherium is the largest terrestrial mammal known. It is a member of the rhinoceros family. Some material was found earlier in the 20th century, but the first fairly complete skull and skeletal elements were found by Roy Chapman Andrews in 1922 while on an expedition for the American Museum of Natural History in Mongolia. Indricotherium would have stood about 16.5 feet (~5 meters) tall at the shoulder and is estimated to have weighed in excess of 20 tons. There were sauropod dinosaurs that were smaller than Indricotherium! This giant was a herbivore and filled a simular niche to the sauropods and modern giraffes, so much so that it is sometimes referred to as the ‘giraffe rhinoceros’. It stripped tall trees bare of leaves using its large front teeth and mobile lips.
In the family tree of mammals Indricotherium is in the order Perrisodactyla (horses, rhinos, and tapirs). Within this group it in the rhinoceros clade. While rhinos today all look pretty much the same their fossil record shows this group used to be extremely diverse, with two completely extinct major sub groupings. Indricotherium is in the group Hyracodontidae (the running rhinos). This lineage divered from that leading to modern rhinos over 55 million years ago. Not all rhinos in this group were giant sized, the very first ones were no larger than wolves! All members of this group lacked horns like Indricotherium.
There is a bit of controversy and confusion surrounding the topic of what genus name to apply to this animal. Indricotherium has been proposed by some workers to be synonymous with Paraceratherium and Baluchitherium, but this is not universally accepted. I have used the name Indricotherium for this entry as both examples shown above are based upon material that has held the name Indricotherium.