Saber-toothed cats: Horrifying genetic defects revealed

A study published in Frontiers in Veterinary Science has documented an extraordinarily high burden of congenital spinal defects and nerve tumors in the saber-toothed cat Smilodon fatalis, evidence the authors argue points to severe inbreeding in the final millennia before the species vanished. The analysis examined more than 3,700 vertebrae recovered from the La Brea tar pits in Los Angeles, representing at least 849 individual cats that lived roughly 12,000 years ago.

Tar pits as a pathological archive

The La Brea asphalt seeps functioned as a natural trap: herbivores mired in the viscous bitumen attracted predators, which then became stuck themselves. This process accumulated thousands of skeletons in stratigraphic layers that span the end of the Pleistocene. For the current study, researchers used computed tomography to scan vertebrae from the collection, screening for developmental anomalies, degenerative changes, and neoplastic growths.

Tumor frequency far exceeds modern benchmarks

The three confirmed spinal nerve tumors translate to an estimated incidence of 353 cases per 100,000 individuals. For comparison, the reported incidence of comparable nerve-sheath tumors in humans is 0.38 per 100,000. The congenital defects — malformed, fused, or asymmetrical vertebrae — were distributed across the sample in numbers that the researchers say cannot be explained by random injury or post-mortem distortion.

Biomechanical consequences for an ambush predator

S. fatalis weighed up to 270 kilograms and relied on a brief, explosive lunge from concealment to bring down large prey. Chronic spinal inflammation, fused segments, and nerve-tumor compression would have produced lameness, muscle atrophy, and an inability to generate the rapid extension required for a killing strike. The authors propose that debilitated individuals, unable to hunt effectively, were disproportionately drawn to the easy but dangerous meals offered by animals already trapped in asphalt — creating a feedback loop that funneled the sickest cats into the fossil record.

Biophysicist Alexey Kornilov added that the observed skeletal deformations directly compromise the biomechanics of locomotion, making a full-powered jump or lunge mechanically impossible for affected animals.

Inbreeding inference without ancient DNA

No soft tissue has survived in the asphalt matrix, so direct genetic testing is not possible. The inbreeding hypothesis rests on the aggregate skeletal signal: a constellation of vertebral malformations, fusions, and rare neural tumors at frequencies that, in living mammals, are hallmarks of small, isolated populations accumulating deleterious recessives. The authors note a parallel in the terminal populations of woolly mammoths, where similar genomic erosion has been documented from preserved DNA.

Questions about the Smilodon findings

Why are so many diseased individuals found in the tar pits?

Weakened cats lost the ability to hunt efficiently and more often risked approaching trapped prey, leading to their own entrapment.

Could these pathologies be random injury rather than genetic?

Statistical analysis shows an anomalously high frequency of congenital defects, making the random-trauma explanation unlikely.

How did the tumors affect hunting?

Such growths cause pain and muscle atrophy, depriving the predator of the explosive pounce required to subdue large prey.

Is inbreeding proven?

Direct DNA evidence is absent because soft tissues did not preserve, but the suite of skeletal anomalies indicates inbreeding as the most probable cause.

Source: This article was adapted from an original Russian-language publication by Pravda.Ru.