Size Mattered to Ancient Bear, Suggestions about Penis Bones

Fossilized penis bones may provide valuable insights into the sexual lifestyles of prehistoric bears, even in the absence of any film.

A recent study examined a set of penile bones from a Spanish bear species that is now extinct. The research discovered that this extinct animal, known as Indarctos arctoides, had a considerable penis bone in comparison to modern bears, suggesting it had long-lasting but rare sex sessions. And the ladies could have evaluated their partners based on the size of their penises.

The penile bone, or bacula, is absent from modern male humans, although it is present in many other animals, such as gorillas and chimpanzees. An animal’s penile bone helps it remain consistently erect during sexual activity, unlike humans, who rely on blood pressure to do the same.

Although penis bones are uncommon in the fossil record, five of this substantial prehistoric bear’s bones were discovered by researchers in Spain’s Madrid Basin. The male of the species would have reached a height of around 584 pounds (265 kilograms), comparable to the size of a European brown bear when the bear inhabited Europe in the Late Miocene, some 12 million to 5 million years ago.

Its bacula measured an average of 9.1 inches (23.3 cm) in length, which is much longer than the penis bones of much larger bears. The biggest bears on Earth today, male polar bears, weigh an average of 1,100 lbs. (500 kg), yet the average length of their penile bone is just 7.3 inches (18.6 cm), according to the study.

The length of the penile bone may provide information regarding the ecological habits and mating system of Indarctos arctoides and its sexual behavior.

The researchers surmise that the bear had fewer but more extended periods of intercourse than other animals based on the size of its baculum. According to the study’s researchers, a lengthy baculum may have provided the female’s reproductive system with physical support during mating, keeping it open and positioned for successful fertilization during these infrequent liaisons.

The researchers speculate that since Indarctos arctoides may have had smaller population densities and comparatively larger individual ranges, there may have been fewer sexual interactions.

According to the fossil record, the male Indarctos arctoides would have been far more significant than the female. According to earlier studies, bear species exhibiting significant sex differences often have shorter penis bones and mating behaviors in which males take many partners and engage in intense competition for females. The comparatively lengthy bacula of Indarctos arctoides implies that it was a sexually chosen characteristic that females used to judge the quality of their partners.

Juan Abella, a paleobiologist from the Autonomous University of Barcelona, led the research. It was described in depth in PLOS ONE on September 18.

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