A dire wolf at the Page Museum. Note the baculum.
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Photo by Brian Switek.
A dire wolf at the Page Museum. Note the baculum.

Broken Baculum a Sign of Painful Ice Age Injury

We’ve all had moments of sympathy pain. That little twinge when we see or hear about a fracture, burn, kick in the groin, or other familiar trauma that hits a little too close to home. And this phenomenon crosses species boundaries. I know because I just read a paleontology paper with an injury that made me clench my jaw and suck the air through my teeth.

The study, written by Adam Hartstone-Rose and colleagues, is titled “The Bacula of Rancho La Brea.” It’s all about Ice Age penis bones. While we lack the genital bones of our ancestors – the baculum in males and baubellum in females — they’re pretty common in other groups of mammals, and paleontologists working at Los Angeles’ famous asphalt seep have pulled hundreds of os penis from the ancient mire.

The bones include specimens from coyotes, weasels, badger, and fox, but dire wolves far outstrip the competition with about 400 hundred bacula, 159 of which are complete. But not all of these bones were in good health. Eight of the dire wolf bacula in the La Brea sample had some kind of pathology. “Most of these demonstrate some degree of twisting along the long axis that may have been either congenital or the result of trauma”, Hartstone-Rose and coauthors write. And of this smaller sample, a few bacula were fractured.

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The broken baculum of a La Brea dire wolf. From Hartstone-Rose et al., 2015.

LACMHC 8291 had an especially rough time of it. The caption accompanying the image reads “A broken, displaced, and healed C. dirus baculum”, meaning that the tip broke and healed in a different position than it started. That was enough to make me cross my legs while reading the paper.

Without what would be one of the stranger sets of time travel coordinates ever, we’ll never know exactly what happened to the poor wolf. The leading hypothesis for such pathologies is that a mating male gets accosted by a rival in the middle of the act, which could “cause the mating male to jump suddenly and snap the bone.”

As cringe-inducing as such injuries may be, though, they were relatively rare among La Brea’s dire wolves. The number of broken bacula is actually lower than expected for the sample size compared to the incidence the same injury in their modern relatives. The size of their bacula, Hartstone-Rose and colleagues suggest, might explain why.

The os penis of adult dire wolves were about 44% longer than those of gray wolves and were significantly more massive. This made it a tougher bone to break. Paired with the unexpected rarity of baculum injuries, the paleontologists propose, this might mean that the modified members of dire wolves were an evolutionary response to competition for mates. So in evolutionary terms, the solution for dire wolves was to walk softly and carry a big stick.


Hartstone-Rose, A., Dundas, R., Boyde, B., Long, R., Farrell, A., Shaw, C. 2015. The bacula of Rancho La Brea. Natural History Museum of Los Angeles County Science Series, 42. pp 53-64