Saber-Toothed Tigers and Dire Wolves Suffered From Bone Disease

Some fossils preserved in the La Brea tar pits showed signs of an inherited joint condition that may have proliferated as the animals neared extinction

a saber-toothed tiger skull, head-on, in a glass case
A saber-toothed tiger skull during a press preview at Sotheby's in July 2022. Alexi Rosenfeld / Getty Images

Saber-toothed cats and dire wolves, two predators that roamed the Earth during the last Ice Age, may have had a high rate of a developmental bone disease, according to a new study of their remains.

Researchers examined hundreds of bones from the extinct animals dug out of the La Brea tar pits in Los Angeles over the last century. The carnivores’ fossils dated to between 12,000 and 55,000 years ago, according to Science’s Celina Zhao.

For some types of bones, between 4 and 6 percent had signs of osteochondrosis dissecans (OCD), a joint condition in which the bone underneath cartilage dies and can break loose due to a lack of blood flow. The high rate of disease could suggest the animals were inbreeding as they went extinct, according to the new paper published Wednesday in the journal PLOS One.

Finding this disease in fossils is “really interesting, because it gives us this sort of holistic look at how these things evolve and how they might change over time,” Ashley Reynolds, an evolutionary ecologist at the University of Ottawa in Canada who did not contribute to the study, tells Live Science’s Ethan Freedman.

A complete skeleton of a saber-toothed tiger on a black background
A skeleton of a saber-toothed tiger from Rio Araco, Argentina. CM Dixon / Print Collector / Getty Images

Tar pits form after crude oil rises to Earth’s surface and the light part of the oil evaporates, leaving just tar behind, according to the University of California, Berkeley. The La Brea tar pits contain well-preserved animals and plants from the Pleistocene epoch, which spanned between 11,700 and 2.6 million years ago. When large herbivores got trapped in the goo, carnivores would follow them in and get stuck as well.

The researchers took advantage of these high-quality fossils, which are now housed at the La Brea Tar Pits and Museum, to study the incidence of OCD in the extinct animals. At least 2,000 saber-toothed cats and 4,000 dire wolves were preserved in the tar pits, according to the paper.

Osteochondrosis affects a wide range of species, from humans to horses. It’s genetically inherited and is found in inbred dog breeds, including border collies and greater Swiss mountain dogs, per Science. But in wild animals, the condition hasn’t been well-studied.

To look for the disease in these extinct predators, the researchers analyzed 88 shoulder bones, 834 thigh bones and 214 shin bones from saber-toothed cats, as well as 242 shoulders, 266 thighs and 170 shins from dire wolves. Because scientists have found little evidence of OCD in modern cats and wild dogs, the team predicted they wouldn’t find a lot of the disease in the tar pit fossils.

But the results showed that 6 percent of the saber-toothed cat thigh bones, 2.6 percent of the dire wolf thigh bones and 4.5 percent of the dire wolf shoulder bones had signs of OCD.

“I think there is no animal [species] today which has a prevalence of 6 percent,” Hugo Schmökel, a co-author of the study and a veterinarian at IVC Evidensia Academy in Sweden, tells New Scientist’s Christa Lesté-Lasserre. “In dogs, we’re talking under 1 percent. In humans, it’s clearly under 1 percent. So that’s amazingly high.”

The bone defects in the saber-toothed tigers were mostly small, and the condition was not often severe. Schmökel tells Science that the animals would have experienced relatively minor pain: a “two or three, with better days and worse days.”

The fossils reveal that bone conditions such as osteochondrosis have long been present in mammals. “We often think of these things as new diseases related to domestication,” Mairin Balisi, a co-author of the study and paleontologist at the Raymond M. Alf Museum of Paleontology who used to work at the La Brea Tar Pits and Museum, tells New Scientist. “But they’re actually in old animals, too. That opens up a lot of new questions, I think.”

The researchers theorize as the predators’ populations dwindled, inbreeding could have raised the prevalence of the bone disease. But with these fossils, that could be a difficult idea to prove: Julie Meachen, a paleontologist at Des Moines University who wasn’t involved in the research, tells Science that it’s hard to know when these animals died, making it unclear whether they faced higher rates of OCD when they drew nearer to extinction.

Editor’s note, August 10, 2023: This article has been updated with a new photograph that more clearly depicts a saber-toothed tiger.

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