Rhinos survived the Ice Age and saber-toothed tigers, but humans may be the greatest threat the horned herbivores have ever faced.

Demand for rhinoceros' horns as folk medicine and ornaments in Asia fuels the illegal slaughter of rhinos. Recently in South Africa, four Kruger National Park workers, including a ranger, were arrested on charges of rhino poaching, reported the AP.

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Last year was the worst on record rhinos in South Africa. A record 448 rhinos were killed in 2011. This year, 80 rhinos have already been killed, reported the AP.

To save the rhinos, wildlife managers have gone so far as to use a chemical which makes the beast's horns toxic to anyone who ingests them.

DNews Rhino Round-Up:

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Black Rhino (Diceros bicornis) – Native to Africa, one subspecies of this critically endangered rhino was declared extinct in 2011.

White Rhino (Ceratotherium simum) – Also native to Africa, the southern subspecies is considered “Near Threatened” by the IUCN, but it's northern cousin is believed to be extinct in the wild.

Indian Rhino (Rhinoceros unicornis) – A few thousand Indian rhinos still browse the foothills of the Himalayas. The species once ranged over the most of the north of the subcontinent.

Javan Rhino (Rhinoceros sondaicus) – The Javan rhino once lived in most of Southeast Asia, as far north as China. But after a remnant population in Vietnam was wiped out, the last toehold of the species is a tiny peninsula on Java in Indonesia.

Sumatran Rhino (Dicerorhinus sumatrensis) – Another Southeast Asian species which now exists only in a few isolated pockets. The rhino clings to life on the Malay Peninsula, Sumatra and Borneo.

IMAGE: White rhineceros, Ceratotherium simum, in Lion County Safari, Florida. (Duncan Rawlinson, Wikimedia Commons)