Above: The Front of the Specimen Card The Hyracodon, one of the oldest relatives of the modern rhino, was a byproduct of the mammalian explosion of diversity in the Eocene. Colloquially known as the “Running Rhino” for its long slender legs, the creature was much smaller than the rhinos we know today and lacked the iconic horn. The North American species settled in what is now the Midwest, where it evolved long legs that let the Hyracodon run through its habitat to avoid predation. They grew to reach about 5 feet in length, making them comparable to a great dane in size. This specimen is a Hyracodon tooth recovered on private land from the White River Formation in South Dakota. The estimated age is 32,000,000 years old. As pictured, the specimen is enclosed in a handsome, glass-topped riker box case measuring 4 1/2" x 3 1/2". A small information card is also included that also serves as the certificate of authenticity.Please Note: Specimens vary widely in size and shape. Some teeth will show more natural wear than others. There may also be cracks, small fissures, or chips in the tooth enamel. This is totally normal for fossils of this type. The pictures included on this page provide an example of the type of tooth you can expect. More About Hyracodons Above: An artist's concept of the Hyracodon echoing the classic painting by Charles M. Knight (Source: Mini Museum). The Hyracodon, one of the oldest relatives of the modern rhino, was a byproduct of the mammalian explosion of diversity in the Eocene. Colloquially known as the “Running Rhino” for its long slender legs, the creature looked quite different from what we think of as a rhinoceros today. No horns sat over their noses, nor were they very big, measuring at about the size of a large dog. However, Hyracodon is still a fascinating animal whose fossils tell us a story of an ancient world.In the mid-Eocene, 48 million years ago, the first members of the Hyracodontidae family emerged in the fossil record in Asia. These creatures eventually spread to North America during a thermal maximum, where they were met with rough forests and steppes.The North American species settled in what is now the midwest, where it evolved long legs that let the Hyracodon run through its habitat to avoid predation. These legs are what’s given the creature its catchy nickname: The Running Rhino. They grew to reach about 5 feet in length, making them comparable to a great dane in size. Above: A fossilized Hyracodon skeleton in the Los Angeles Natural History Museum (Source: Dawn Pedersen/Flickr). Each of their feet had 3 toes with a hoof-like appearance and they evolved long snouts that made their heads quite large in proportion to their bodies. Between its hoof-like feet and elongated heads, Hyracodon resembled the primitive horses, Mesohippus, with which it would have been a contemporary of. Above: Sample Hyracodon Teeth. The rather simple, flat teeth of early Hyracodons lead scientists to suggest that they initially followed a diet of leaves and foliage, which would make sense with their forest homes. However, as time went on some later fossils show a more complex molar, which may indicate a shift in diet from browsing for leaves to grazing low grasses. A close relative of Hyracodon is the Paraceratherium, the largest land mammal to ever walk the Earth! Paraceratherium had a shoulder height of an enormous 16 feet and may have weighed over 20 tons. Like Hyracodon, this creature was a hornless member of the rhino family, though it certainly wasn’t as quick on its feet! Above: A comparison of living rhino species and extinct, gigantic relatives. (Source: WikiMedia) Hyracodon’s extinction towards the end of the Oligocene, nearly 20 million years after their first appearance. This marked the end of the running rhinos, with modern rhinoceroses being much larger in stature. Further Reading Rhinoceros Giants: The Paleobiology of Indricotheres, by Donald R. Prothero, Indiana University Press, 2013.“RHINOCEROS GIANTS: THE LARGEST LAND MAMMAL PARACERATHERIUM.” The Story of Life in 25 Fossils: Tales of Intrepid Fossil Hunters and the Wonders of Evolution, by Donald R. Prothero, Columbia University Press, NEW YORK, 2015, pp. 314–325.“LAURASIATHERIA: PERISSODACTYLA.: ‘Odd-Toed’ Hoofed Mammals: Horses, Rhinos, Tapirs, and Their Extinct Relatives.” The Princeton Field Guide to Prehistoric Mammals, by Donald R. Prothero and Mary Persis Williams, Princeton University Press, Princeton; Oxford, 2017, pp. 186–202. Above: Back of the Specimen Card
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