The most obvious and distinguishing characteristic of a rhino is its large one or two horns above the nose. These damned horns have been bringing their death by human hands because many cultures price them for their supposed magical or medicinal qualities. And those medicines have the same effect like chewing your nails ... (as we'll see further on). In other cultures (like in Yemen or Oman), flaunting dagger handles of rhino horn are a sign of health...

Sad final for these odd and interesting beasts that survived so many geological eras just to end like this. In fact, two rhino species (wholly rhino and giant unicorn) from Eurasian steppes might have been wiped out by humans, and all current species are amongst the most endangered big animals.

Rhinoceros horns have not only a unique position, but also a unique composition and structure, because they are made only of keratin. Horns of other mammals, like cattle, giraffes, antelopes, sheep, goats, gazelles or pronghorn, have a bony core covered by a sheath of keratin. Keratin is the same substance found in nails, hair, wool, bird feather, reptile scales, or in the outer layer of vertebrate skin.

New research at Ohio University explains how the rhino horn gets its distinctive curve and sharply pointed tip. Using CT scans, researchers at Ohio University found dark dense patches of mineral deposits of calcium and melanin in the centers of the horns. The calcium deposits strengthen the horn core, and the melanin pigments protect it from breakdown by the solar UV rays. The rhino horn structure is like that of a pencil, with a tough core and a weaker outer layer, which allows the horns to be honed to a sharp point. The soft outer part of a rhino horn is degraded by sun exposure and worn into its sharpened shape when the beasts clash horns with one another and by being rubbed on the ground and vegetation. Not used, the horns would look more like cylinders.

The study also explains why the horns get curved: "Because the keratin in the front grows a little bit faster than the keratin in the back," said study leader Tobin Hieronymus, an OU doctoral student. "Most rhino horns curve backwards, but every now and then you'll see one that curves forward. Some of them even change curve directions halfway up, all from slight differences in growth rate. Fingernails will curve for the same reason, if you grow them long enough," said Tobin Hieronymus, a doctoral student in biological sciences.

So the rhinoceros horns are not just clumps of modified hair. "The horns most closely resemble the structure of horses' hoofs, turtle beaks and cockatoo bills. This might be related to the strength of these materials, although more research is needed in this area," told Hieronymus.

Melanin and calcium patches appear in yearly growth but the effects of environmental factors like temperature, diet and stress on the growth are still unknown. "Ultimately, we think our findings will help dispel some of the folk wisdom attached to the horn. The more we can learn about the horn, the better we can understand and manage rhino populations in the wild and in captivity," said Lawrence Witmer, a professor of anatomy in Ohio University's College of Osteopathic Medicine.

Image credit: Ohio University