If you think this is a mammoth ivory, you're totally wrong! It is the penis bone belonging to an extinct walrus species!

The penis' main function is to keep enough stiffness to penetrate an orifice during mating, and to deliver sperm. And mammals found the best solution - most of them have this unique bone named baculum (penis bone, penile bone or os penis) inside their penis. The sole mammals lacking baculum are the humans, horses, donkeys, rhinoceros, marsupials, rabbits, cetaceans (whales and dolphins), elephants and hyenas.

The baculum is kept in the abdomen and, when required, a set of muscles move it into a sheath in the soft tissues of the penis, offering stiffness during the copulation. The baculum's size and shape varies depending on species and the largest baculum belongs to the walrus, where it can be as long as 30 inches (75 cm): the size of a human femur!

The mummified baculum you see in the photo comes from a species of walrus extinguished 12,000 years ago. It has a length of 4 ft (1.2 m), a dramatic curve to its tip and is covered with weathered skin and dry muscle tissue. In modern walruses, the baculum is straight, not curbed.

When discovered, the bone was mistakenly taken for a badly weathered mammoth tusk, and was going to be polished. Luckily, an experimented fossil dealer recognized what it was before any cosmetic improvements. Buried in the frozen tundra for tens of millenia, the skin and flesh covering the baculum have dried, resulting this amazing preservation.

The huge fossil penis bone was sold in August at the I.M. Chait Gallery natural history auction for $ 8,000 to a Ripley's Believe It or Not museum. "Size matters, and the walrus has got everybody beat," said Josh Chait, operations director for his family's auction house in Beverly Hills.

In Alaska, walrus baculums are called "oosiks", and are polished and transformed into knife handles sold to tourists. The fossil baculum was discovered preserved in permafrost in northern Siberia while the prospectors were searching for mammoth tusks. This is the largest known fossil penis bone encountered so far. "I'm glad it's going to a museum and not a private collection so it can on public display. It's definitely something everyone should see once in their life.", Chait said.