Saber-Toothed Cats’ Spinal Tumors Reveal How Inbreeding Threatened Survival

Saber-toothed cats (Smilodon fatalis) from the La Brea Tar Pits preserve more than just bones—they also retain a medical record of what may have been their final, precarious days. A new analysis of fossil spines suggests an unexpectedly high occurrence of spinal nerve tumors, a condition that could have impaired movement and intensified pain-related behavior.

The work, published in Frontiers in Veterinary Science, focuses on vertebral pathology in thousands of museum specimens. Using observational methods, the researchers cataloged developmental abnormalities and examined vertebrae for structural signatures consistent with tumor growth over time.

At the La Brea Tar Pits, crude oil seeps upward and forms sticky tar that traps animals. Prey inside the tar emit distress signals that attract predators, and those predators can become trapped as well. This recurring cycle created a deadly feedback loop during the Pleistocene, affecting carnivores including Smilodon.

The study identified extensive skeletal irregularities: vertebral arches that never fully formed, multiple fused “block” vertebrae, and “transitional” vertebrae where regions adopt incorrect shapes—such as cervical vertebrae developing rib-like features. Such developmental disruptions point toward population-level biological stress during growth.

More strikingly, three vertebrae from separate tar-pit locations showed foramina—nerve passage openings—whose enlargement and smooth remodeled margins strongly indicate spinal nerve tumors. The logic is mechanical: as a tumor expands and presses on surrounding tissue, it increases the size of the bone opening.

Spinal nerve tumors are rare in living species and humans, where incidence is on the order of fractions per 100,000 people. In Smilodon, the presence of three affected animals among the available fossils implies a prevalence far higher than expected, estimated at roughly 353 cases per 100,000 cats.

The researchers caution that the tumor history cannot be confirmed without genetic testing, but the pattern of malformations supports the hypothesis of inbreeding near extinction. When population sizes shrink, harmful variants can become concentrated, increasing the probability of inherited developmental problems.

They also consider behavioral pathways: tumors may have increased pain and reduced hunting efficiency, which could have made already-challenged animals take greater risks—potentially making them more likely to wander into tar-laced traps.

Finally, the study frames these findings as a warning for modern wildlife. Habitat loss, pollution, hunting, and poaching reduce populations and then amplify medical consequences such as inbreeding, making recovery harder once numbers are already depleted.