Many male mammals have a bacula, also known as a penis-bone, to assist in reproduction. The stiffness of the bone allows for easy insertion of the penis into the female’s vagina (as contrasted with blood pressure to maintain an erection as occurs with humans.) All bears have a bacula, but what sets I. arctoides apart from modern species was its size. Scientists have found many fossil bones from the bears and thus have a clear idea of its overall size. The bear was on average about the size of modern European Brown bears (265.74 kg for males and 137.30 kg for females), yet its bacula was longer than the much larger Polar or Kodiak bears that exist today. Four of the five specimens found were from adult males—together their baculum averaged 225.26 mm in length.
Bacula finds are rare in archeological research, their thinness makes them prone to breaking, and quite often they are mistaken for rib bones. Thus finding 5 wholly intact specimens was a noteworthy find in and of itself—that they represent such a large penis bones relative to body size is perhaps even more remarkable.
Read more at: Phys.org