Saber-toothed cats became inbred—and struggled to move—before they went extinct
Population declines led to spike in spinal deformities and rare tumors, fossil study suggests
27 Jul 2026 - 12:00 AM ET By Taylor Mitchell Brown
About 14,700 years ago, a large cat hobbled through what is now the heart of Los Angeles, toward the panicked cries of a camel trapped in tar. But as the fearsome feline approached the hapless herbivore, it, too, became ensnared in the pit of burbling oil—condemning itself to a similar fate.
Why were these saber-toothed felines drawn to the pits? One reason, researchers now suggest, is that picking off trapped prey may have been the cats’ only reliable way to hunt: Many had hampered mobility, a side effect of heritable deformities and rare nerve tumors brought on by generations of inbreeding. The work, published today in Frontiers in Veterinary Science, provides one of the first direct indicators of how North America’s megafauna suffered the consequences of population decline through the end of the last ice age.
“Fossil evidence of inherited disorders is uncommon,” says Federico Agnolín, a paleontologist and saber-toothed cat expert at the Argentine Museum of Natural Science who was not involved with the research. “Documenting a possible increase in developmental abnormalities and rare tumors offers new perspective on the biological consequences of population decline before extinction.”
The new work focuses on thousands of saber-toothed cat vertebrae recovered from the La Brea Tar Pits in Los Angeles. The pits, which are filled with viscous crude oil seeping from the earth, have trapped many species over the past tens of thousands of years, including everything from American camels and giant ground sloths to dire wolves and saber-toothed cats such as Smilodon fatalis. Carnivores and herbivores alike became stuck in the sludgy black tar and died.
S. fatalis, which went extinct about 12,000 years ago, was one of this ecosystem’s top predators. The cat ranged in size from 160 to 280 kilograms and was likely an ambush predator, pouncing on unsuspecting grazers and biting into them with saber-shaped canines more than 20 centimeters long. Yet S. fatalis also seemed to have a knack for getting trapped in tar, says Emily Lindsey, a paleontologist at La Brea who was not involved with the work. It’s the second most commonly retrieved large mammal from the pits.
The study’s lead author Hugo Schmökel, a veterinary surgeon and researcher at the University of Zurich, saw these bones for the first time while visiting La Brea to research dire wolves, another common predator species at the site. He noticed many of the vertebrae in the museum’s Smilodon collection had abnormalities like those he sees in today’s cats and dogs. “My eyes are trained by thousands of CT scans from my patients,” Schmökel says.
To tease out more from the bones, Schmökel and his colleagues scrutinized 3722 vertebrae of S. fatalis, representing at least 849 adults. The analysis revealed an abundance of congenital deformities, including 48 fused vertebrae and 32 incompletely developed vertebral arches. But the analysis also uncovered evidence of three exceedingly rare spinal nerve tumors, which grow in the vertebrae and form dumbbell-shaped cavities in the bone.
Spinal nerve tumors are extraordinarily rare among today’s large mammals, occurring in fewer than one out of 100,000 modern humans. Yet Schmökel’s analysis suggests that among the La Brea Smilodon, a staggering 353 in every 100,000 individuals had the tumors.
The team suspects these deformities and tumors indicate a lengthy history of inbreeding, which would have allowed harmful mutations to build up in the cats’ genomes and increase the likelihood of congenital deformities. Based on his surgical practice, Schmökel thinks the malformations would have become debilitating as the animals aged, based on the resemblances to equivalent deformities he’s seen in dogs. “Young dogs show no clinical signs, but later in life, the secondary degenerative processes start to be painful and slow them down,” he says. “Some must have been painful over time.”
For Schmökel and Lindsey, the new results serve as a portent for modern animals suffering population loss from habitat degradation and climate change. “It’s what we see in large carnivore populations today that are under stress,” Lindsey says. “Your population’s decreasing, and that leads to inbreeding, which makes you less able to respond to any kind of perturbation because you’re losing that genetic diversity that evolution can play with.”
The newly uncovered diseases within Smilodon, she adds, point to just how vicious that cycle can get. For one of the ice age’s most iconic predators, “things might have been getting really bad at the end.”
doi: 10.1126/science.zn09lc2
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Taylor Mitchell Brown
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Taylor Mitchell Brown is a journalist based in San Diego.
