Rare spinal tumours in sabre-toothed cats may offer clues to their extinction

New research on fossils from California's La Brea Tar Pits suggests that inbreeding and spinal diseases may have contributed to the extinction of sabre-toothed cats, offering fresh insights into the decline of one of the Ice Age's most iconic predators.

The study, published on July 27 in Frontiers in Veterinary Science, examined more than 3,000 vertebrae from Smilodon fatalis and identified hundreds of spinal abnormalities, including an unusually high number of rare tumours that researchers believe may have become more common as the population declined, according to ScienceNews.

The fossils, preserved in the asphalt-filled La Brea Tar Pits in Los Angeles, have long provided scientists with a detailed record of extinct species, including mammoths, dire wolves, bison, and sabre-toothed cats.

Veterinary spine surgeon Hugo Schmökel of the IVC Evidensia Academy in Stockholm first noticed signs of spinal disease while studying fossils from the collection.

"As a spine surgeon for dogs and cats, I was immediately interested and went back twice to La Brea," Schmökel said.

Using visual examinations and X-ray scans, Schmökel and his colleagues found a range of spinal deformities, including fused vertebrae and abnormally split bones. Three sabre-toothed cats exhibited an especially rare condition in which small openings in the lower vertebrae had expanded into large cavities caused by slow-growing tumours on spinal nerves.

Such tumours are extremely rare in modern humans, but the researchers estimated they occurred about 1,000 times more frequently in the La Brea sabre-toothed cat fossils. They cautioned, however, that the findings may not represent the broader population.

The tumours would likely have caused chronic pain, potentially making hunting more difficult for the predators.

Palaeontologist Mairin Balisi of the Raymond M. Alf Museum of Palaeontology said the cats' hunting strategy may have worsened the effects of the condition.

"It would have required bracing on their hind legs, pulling back and then launching themselves at their prey," Balisi said.

She added that their prey, including large animals such as bison, "would not go down peacefully," placing considerable strain on the cats' lower backs.

The researchers suggest the high rate of spinal disorders may have resulted from inbreeding as sabre-toothed cat populations became smaller and more isolated near the end of the Pleistocene Epoch. Similar skeletal abnormalities have been documented in inbred modern grey wolf populations and in other extinct mammals before their disappearance.

Two of the three fossils with spinal tumours date to between 12,000 and 13,000 years ago, shortly before the species became extinct.

Balisi said the findings illustrate how shrinking populations can enter a cycle of genetic decline.

"This might be how extinction happens."

Researchers said definitive proof will require genetic evidence, but usable DNA has not yet been recovered from the La Brea sabre-toothed cat fossils.

By Sabina Mammadli