Illustration of the smilodon, or saber-toothed tiger, which became extinct about 10,000 years ago
ROMAN UCHYTEL/SCIENTIFIC PHOTO LIBRARY
Saber-toothed tigers and dire wolves that lived in the last Ice Age had a surprising amount of inherited bone disease, which could reflect inbreeding as the ancient carnivores approached extinction about 10,000 years ago.
More than 6 percent of the femurs of the tigers pulled from the La Brea tar pits in Los Angeles showed the telltale nicks and holes of osteochondrosis — a prevalence at least six times higher than that in modern mammal species.
“I think there is no animal [species] today, which has a prevalence of 6 percent,” says Hugo Schmokel at the IVC Evidensia Academy in Stockholm, Sweden. “In dogs, we are talking about less than 1 percent. In humans, it is clearly less than 1 percent. So that is astonishingly high.”
Osteochondrosis occurs when small areas of growing bone fail to form, leaving holes that can cause pain and a limp. Although rare, the disease affects most mammalian species and often runs in families or in specific breeds. Nine percent of border collies, for example, have osteochondrosis in the shoulders, while the disease is essentially absent in many other dog breeds. Modern cats almost never develop osteochondrosis, although a few cases have been found in captive snow leopards that are genetically related.
Schmökel, an orthopedic veterinarian specializing in cats and dogs, says she always enjoyed it looking at ancient carnivorous skeletons in natural history museums and eventually began to wonder if they had the same kinds of bone diseases as his modern patients.
He reached for Mairin Balisi at the Raymond M. Alf Museum of Paleontology in Claremont, California, to access the museum’s large collection of specimens from the museum’s tar pits. There he carefully examined 1163 leg and shoulder bones of saber-toothed tigers (Smilodon fatalis) and 678 leg and shoulder bones of dire wolves (Aenocyon dirus), then took X-rays of some bones.
Schmökel and his colleagues found that 6 percent of the saber-toothed tiger’s femurs had osteochondrosis lesions. Most of the lesions were less than 7 millimeters in diameter, but a third were up to 12 millimeters in size – although these were still not considered large or serious. These lesions were likely too mild to cause pain or affect movement in most animals, Schmökel says.
![](https://images.newscientist.com/wp-content/uploads/2023/07/12154320/SEI_163813137.jpg?width=1200)
Lesions in the femurs of saber-toothed tigers from the La Brea tar pits in Los Angeles
Schmökel et al., 2023, PLOS ONE, CC-BY 4.0
As for the dire wolves, the researchers found most lesions in the shoulder joints, with a prevalence of 4.5 percent, consisting mainly of small lesions. But 2.6 percent of the wolf femurs also had osteochondrosis, and in these cases, most of the lesions were considered large — over 12 millimeters — though not serious.
“We often think of these things as new diseases related to domestication,” says Balisi. ‘But they are actually also in old animals. That raises a lot of new questions, I think.”
The bones span a wide range of dates, from about 55,000 to 12,000 years ago, shortly before the two species became extinct. It makes sense that the high rates of hereditary disease are related to inbreeding as their populations decline, says Balisi, and hopes to confirm this in the future.
“I think it’s only a matter of time before we can extract DNA from the targets. And I wouldn’t be surprised if that reflects these animals becoming more and more inbred,” she says.
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