Fossils recovered from the La Brea Tar Pits in Los Angeles reveal that extinct saber-toothed cats suffered from a high frequency of spinal maladies, including a rare bone tumor that may point to inbreeding during the twilight years of the species. According to a study published July 27 in Frontiers in Veterinary Science, researchers analyzed over 3,000 vertebrae from Smilodon fatalis and discovered extensive skeletal deformities dating back to the late Pleistocene Epoch.
Spinal Pathologies and Rare Tumors in Smilodon
Crude petroleum oozes from the ground at the La Brea Tar Pits, forming asphalt-rich ponds that ensnared prehistoric wildlife for millennia. Alongside mammoths, dire wolves, and bison, the site preserved the bones of hundreds of saber-toothed cats. Hugo Schmökel, a veterinary surgeon at the IVC Evidensia Academy in Stockholm, examined this collection after initially studying joint diseases in dire wolves.
Schmökel and his colleagues used visual inspections and X-ray scans to analyze more than 3,000 vertebrae, primarily from the lower back. The team documented hundreds of structural anomalies, including fused bones and abnormally split shapes. Among these specimens, three individual cats exhibited an exceptionally rare condition. Small foramina—the tiny holes that permit nerves and blood vessels to pass through vertebrae—were inflated into cavernous hollows. According to the study, modern humans and dogs develop similar bone hollows due to slow-growing tumors on spinal nerves.
Comparing Rates of Spinal Tumors in Prehistoric Predators
In modern human populations, spinal nerve tumors are exceedingly rare, occurring at a rate of roughly 0.38 cases per 100,000 individuals. By contrast, the researchers calculated that the frequency of these tumors among the analyzed saber-toothed cat collection reached approximately 1,000 times that rate. However, study authors caution that this elevated frequency might reflect the unique collection dynamics of the tar pits rather than a universal baseline for the entire species.
These spinal growths would have caused significant physical pain, a factor likely compounded by the hunting mechanics of Smilodon fatalis. Mairin Balisi, a paleontologist at the Raymond M. Alf Museum of Paleontology in Claremont, California, notes that the cats relied on a predatory strategy requiring them to brace on their hind legs, pull back, and launch themselves at heavy prey such as bison. Because such large prey resisted capture, physical grappling placed intense mechanical stress on the lower back. Consequently, debilitated cats experiencing severe spinal pain may have been more vulnerable, driving them to target easier prey and increasing their risk of becoming trapped in the asphalt.
Inbreeding and the Pleistocene Extinction Timeline
The research team suggests that the high prevalence of spinal tumors and related skeletal deformities stems from inbreeding as wild populations dwindled. Similar spinal anomalies appear in modern, isolated gray wolf populations experiencing genetic constriction. Furthermore, DNA and skeletal data from other Pleistocene mammals—including woolly rhinos, mammoths, and giant deer—show parallel signs of inbreeding immediately prior to their extinctions.
Significantly, two of the three Smilodon fossils exhibiting spinal tumors date back 12,000 to 13,000 years, aligning closely with the final disappearance of the species near the end of the Pleistocene Epoch. A prior 2023 study co-authored by Schmökel also documented high rates of bone disease in saber-toothed cat limbs, potentially linked to the same genetic factors.
While researchers have yet to extract usable DNA directly from La Brea’s saber-toothed cat remains, Balisi emphasizes that recovering genetic evidence remains the critical next step for confirming population isolation and inbreeding as drivers of the extinction event.
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