This Arctic bone can measure 22 inches—guess the species

The Baculum: An Ancient Mammalian Feature

The baculum, or os penis, is a bone found in the penis of many mammal species, from bats and rodents to primates and marine mammals. Unlike humans and most ungulates, walruses belong to a lineage that retained this skeletal element through millions of years of evolution. The walrus baculum can reach 22 inches in length and weigh up to two pounds, making it the largest among all mammals. Scientists believe the baculum evolved to provide structural support during prolonged copulation, especially in species where mating occurs in challenging environments. For walruses, this means frigid Arctic waters where maintaining position and endurance is vital. The bone's density and length also correlate with reproductive success: males with larger bacula tend to dominate breeding territories and attract more females during the mating season, which runs from January through March.

Mating Rituals in the Arctic Ocean

Walrus mating takes place in the icy waters of the Bering and Chukchi Seas, where males compete fiercely for access to females. A dominant bull may mate with multiple females in a single season, and each coupling can last over an hour. During this time, the baculum provides critical support, allowing the male to maintain copulation despite the cold and the physical demands of treading water. Males also use elaborate displays—bellowing, tooth-clicking, and underwater vocalizations—to attract females and ward off rivals. The baculum's size is a visible indicator of a male's age and health, and females appear to select mates based on these secondary sexual characteristics. Researchers observing walrus colonies in Alaska and Svalbard have documented that older bulls with the longest bacula hold the prime breeding spots on ice floes and in shallow coastal waters, where females gather to give birth and nurse their young.

Cultural and Scientific Value of the Baculum

For centuries, Indigenous Arctic peoples have harvested walrus bacula for practical and ceremonial purposes. The Yupik and Iñupiat of Alaska carved the dense bone into knife handles, harpoon toggles, and amulets believed to confer strength and virility. Museums across the Arctic, including the University of Alaska Museum of the North in Fairbanks and the Tromsø Museum in Norway, house collections of carved bacula dating back hundreds of years. In the 19th century, European whalers and traders also collected walrus bacula as curiosities, and Victorian collectors prized them for their size and rarity. Modern scientists study the baculum to understand sexual selection and the mechanics of reproduction in marine mammals. Biologists at the University of Alaska Fairbanks have used CT scans to analyze the internal structure of walrus bacula, revealing growth rings that provide insights into age, health, and environmental conditions during the animal's life.

Why the Baculum Still Matters Today

The walrus baculum offers a window into the evolutionary pressures that shaped mammalian reproduction over millions of years. As climate change reduces Arctic ice cover, walrus populations face new challenges: shrinking breeding habitat, increased human activity, and shifts in prey availability. Understanding the role of the baculum in mating success helps conservationists assess population health and reproductive viability. The U.S. Fish and Wildlife Service and the International Union for Conservation of Nature monitor walrus populations in the Bering, Chukchi, and Laptev Seas, where an estimated 200,000 to 250,000 walruses remain. Researchers also track the illegal trade in walrus ivory and bone, as demand for carved bacula persists in black markets across Asia and Europe. By studying this ancient anatomical feature, scientists gain a deeper appreciation for the complex interplay between biology, environment, and culture in one of the planet's most extreme ecosystems.