Foraminal widening indicating a spinal nerve tumor in the saber-tooth cat Smilodon fatalis from Rancho La Brea

Tracing the health of extinct populations is important. Documenting this in deep time is challenging, but skeletal markers of disease can be preserved in fossils. Notably, a high incidence of spinal malformations has been recorded among specimens found in the La Brea Tar Pits, possibly because of an accumulation of expressed deleterious alleles that caused disturbances in developmental processes. The exceptional preservation of hundreds of specimens of the La Brea saber-toothed cat Smilodon fatalis allows us to examine pathologies within and across populations, with dire wolves from the same site and extant large-bodied felids serving as a basis for comparison. We identified three vertebral specimens from S. fatalis with changes indicating a possible spinal nerve tumor (SNT). The prevalence-like estimate was 353 per 100,000 individuals. The observed prevalence of foraminal widening compatible with presumed SNT among the La Brea S. fatalis sample appears high relative to reported human incidence estimates of 0.22-0.38 per 100,000 individuals, although these values are not directly comparable because the fossil estimate reflects skeletal occurrence in a taphonomically biased assemblage rather than clinical incidence. The reason for this high incidence in Smilodon fatalis is unclear, but in humans, many SNTs are associated with genetic mutations. Due to the presumed inbreeding toward the end of the species' existence, a similar mutation could have contributed to the development of the presumed SNTs in S. fatalis.