Saber-toothed tigers had a serious bone disease – 07/19/2023 – Science

Between 50,000 and 10,000 years ago, when ice caps melted and the planet’s temperature rose, around 100 species of giant animals began to disappear without a trace.

Paleontologists have sought to understand exactly how these animals, including iconic predators like the saber-toothed tiger and dire wolf, disappeared. Some hypotheses suggest that the cause was fierce competition for limited food, exacerbated by the arrival of humans and gray wolves. But new evidence suggests that a bone disease that can debilitate modern dogs and cats, and even humans, may also have played a role.

In an article published last week in the journal PLoS One, researchers wrote that as climates change, the bones of saber-toothed tigers and dire wolves have become riddled with defects linked to costochondritis dissecans, or OCD, a serious disease of the development in which bony holes form caused by developing tissue that never hardened. In a living animal, the holes are filled with flaps of cartilage, which can result in painful inflammation.

These findings reveal a fossilized snapshot of how the physiology of key Pleistocene predators likely weakened under environmental pressures, said Mairin Balisi, curator at the Raymond M. Alf Museum of Paleontology in Claremont, Calif., and one of the authors of the paper.

OCD is a common orthopedic disease that affects the joints of fast-growing dogs. It is less common among cats, but cases have been reported among snow leopards. For Hugo Schmokel, a veterinary orthopedic surgeon residing in Stromsholm, Sweden, and one of the authors of the article, this may indicate that OCD is underreported in wild animals.

Schmokel visited the La Brea Tar Pits paleontological research site in Los Angeles in 2022 to study whether saber-toothed tigers and dire wolves suffered from cruciate ligament diseases. Instead, something else caught his eye: indentations of various sizes dotted across the knee and shoulder joints of these ancient carnivores.

Paleontologists had noticed these defects, “but no one had realized that they were perhaps bone injuries sustained in life, not postmortem,” Schmokel said.

With the help of Balisi, then a postdoctoral researcher at the La Brea Tar Pits, and Aisling Farrell, a senior collections administrator, Schmokel examined more than 1,000 limb bones from saber-toothed tigers and dire wolves.

The team found that about 6% of the limb bones of young adult saber-toothed tigers and cubs, specifically the knee joints, had indentations measuring less than seven millimeters.

Nearly 3% of young adult dire wolves and pups also had defects in the knee joint that tended to be larger, measuring more than 12 millimeters. Small joint defects in the shoulders were more common in wolves as well as in dogs, totaling almost 5%. A few limbs from adult animals, but none from puppies, showed signs of osteoarthritis, a degenerative joint disease that can be due to OCD.

The prevalence of the disease among animals appeared to be higher than among modern animals and humans, Schmokel said.

Based on the bones alone, it’s difficult to gauge why OCD struck the animals this way. Nor can the researchers say with certainty how it affected the animals’ quality of life or mobility. In modern domestic animals, the disease can cause varying degrees of pain and lameness. Early in life, these bone defects may disappear on their own; it is possible that they were nothing more than a mild problem, at least for some individuals. It’s also possible that the animals’ social behavior mitigated the worst of the disease, said Larissa DeSantis, a paleontologist at Vanderbilt University who was not involved in the study.

She said in an email that other specimens from the La Brea Tar Pits showed signs of “hip dysplasia and severe arthritis, revealing the ability of these Ice Age predators to live for extended periods of time with these injuries.”

For the researchers, however, the higher prevalence of OCD justifies speculation that perhaps there was an inbreeding problem between saber-toothed tigers and dire wolves, due to their isolated and dwindling populations. Schmokel points to modern animals like Isle Royale wolves and Florida panthers that have experienced the same problem.

DeSantis doesn’t believe OCD was the sole cause of the extinction of these alpha predators, but Balisi says the findings point to the need for more research.

For her, the signs of the disease “may be a morphological manifestation of something deeper that we still don’t know what it is, but I think it’s just a matter of time”.

^{Translated by Clara Allain}