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Known today for their large size and impressive horns, these animals have taken many forms over many millions of years. From horse-like runners to hippo-like waders to gargantuan behemoths, this episode we discuss the incredible evolutionary history of Rhinos.
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Rhinos, with their large bodies, massive heads, and nose horns, are among the most iconic and recognizable animals on Earth. As part of the “odd-toed ungulates” (Perissodactyla), they are close cousins of tapirs and horses. Modern rhinos are found in Africa and Asia, they are all herbivorous, they live mostly solitary lives, and sadly they are all under severe threat of endangerment and extinction, with numerous subspecies considered extinct and two whole species currently restricted to single countries.
Like other perissodactyls, rhinos have an exceptional fossil record that provides an excellent picture of their evolutionary history, all the way back to the earliest perissodactyls of the Eocene. Modern rhinos all belong to the family Rhinocerotidae, but their extended family, the Rhinoceratoidea, includes a number of other major groups.
The earliest rhinos were nearly indistinguishable from the earliest horses and tapirs. From those small herbivores arose a few major groups. These include the Hyracodontidae, sometimes called the “running rhinos,” which were small- to medium-sized animals with long legs and slender bodies well-adapted for getting around quickly; the Amynodontidae, which included some very tapir-like rhinos as well as hippo-like rhinos sometimes nicknamed “aquatic rhinos” or “swamp rhinos,” which are thought to have been semi-aquatic; and Paraceratheriidae (or indricotheres), the “giant rhinos” whose largest members stood over 6 meters (20 feet) tall at the shoulder and weighed 15-20 tons, making them some of the largest land mammals in history, rivaled only by the very biggest ancient elephants.
These diverse groups did well during the Eocene and Oligocene Epochs, but they were all extinct or nearly so by the start of the Miocene, leaving only the Rhinocerotidae, which would eventually include modern rhinos. Within this group, we see the evolution of numerous grazing specialists, hippo-shaped forms (like Teleoceras), large-bodied forms on par with the largest living species, and the origin of these animals’ most famous feature: horns.
Rhinos were extremely diverse during the Miocene Epoch, but they’ve been in decline ever since. At the end of the Miocene, they disappeared from North America, and then at the end of the Pleistocene, they vanished from Europe and northern Asia as well. In the past couple of centuries, human activity has continued to dramatically reduce the populations of the five remaining species of this once-dominant family of large mammals.
Rhino-Like Horny Beasts
The familiar rhino profile – a large body with thick limbs and nose horns – is not exclusive to rhinos. Several other groups evolved a similar appearance, easily mistaken for true rhinos. These included brontotheres, a group of perissodactyls that thrived during the Eocene; uintatheres, an even earlier group of large herbivores that exhibited very ostentatious skulls; and the enigmatic embrithopods, whose one famous rhino-like member, Arsinoitherium, sported a pair of enormous nose horns. Unlike true rhinos, the horns of these animals all featured bony cores, whereas modern rhinos’ horns are made only of keratin, with no major bony component.
More to Learn
Find lots of information about rhinos, modern and ancient, at the Rhino Resource Center
Learn more about rhino conservation on the IUCN Red List and the International Rhino Foundation
Some technical papers about rhino and perissodactyl evolution:
Deng et al 2021
Liu et al 2021
Steiner & Ryder 2011
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The wooly rhino skeleton photo looks like it has bony horns?? Is that actually preserved keratin?
Woolly rhino horns are keratin, not bone, just like modern rhinos. There have been woolly rhino horns found preserved in permafrost! That’s probably the case with the specimen in that photo.