Skeletal disease may hamper the behavior of large predators both living and extinct. In new research, paleontologists from Evidensia Academy and the La Brea Tar Pits and Museum investigated the prevalence of osteochondrosis dissecans, a developmental bone disease affecting the joints, in two Ice Age predators: the saber-toothed cat (Smilodon fatalis) and the dire wolf (Aenocyon dirus, formerly Canis dirus). All fossilized specimens came from the Rancho La Brea fossil locality in Los Angeles, California, the United States.
Osteochondrosis is an orthopedic disease caused by a failure of the endochondral ossification in the epiphyseal plate and joint cartilage in a variety of species ranging from horses to humans.
It is associated with the complex of developmental orthopedic pathologies, causing lameness in advanced cases.
One manifestation of osteochondrosis is osteochondrosis dissecans, which is considered in the failure of cellular differentiation in growing cartilage, leading to its thickening or retention.
“While developmental skeletal diseases like osteochondrosis are well documented as markers of health in domestic animals, fewer studies have examined the extent to which they affect wild animals, even in captivity,” said Evidensia Academy researcher Hugo Schmökel and his colleagues.
“Radiographic examination of living wild animals is costly; and, to our knowledge, only a few institutions house wildlife skeletal postcranial collections large enough to permit reconstructing the prevalence of osteochondrosis or other developmental skeletal disorders in a population.”
“However, developmental skeletal diseases have been suggested to impact Smilodon fatalis, at least 2,000 individuals of which are preserved together with at least 4,000 individuals of Aenocyon dirus at the Rancho La Brea asphalt seeps in Los Angeles, California.”
In the new study, Dr. Schmökel and co-authors examined over 1,000 limb bones of Smilodon fatalis and over 500 limb bones of Aenocyon dirus from La Brea Tar Pits, finding small defects in many bones consistent with osteochondrosis dissecans.
These defects were mainly seen in shoulder and knee joints, with an incidence as high as 7% of the examined bones, significantly higher than that observed in modern species.
The study is limited to isolated bones from a single fossil locality, so further study on other fossil sites might reveal patterns in the prevalence of this disease, and from there might shed light on aspects of these animals’ lives.
It remains unclear, for example, whether these joint problems would have hindered the hunting abilities of these predators.
Furthermore, osteochondrosis dissecans is commonly seen in modern domestic dogs which are highly inbred, so it’s possible that the high incidence of the disease in these fossil animals could be a sign of dwindling populations as these ancient species approached extinction.
“This study adds to the growing literature on Smilodon fatalis and Aenocyon dirus paleopathology, made possible by the unparalleled large sample sizes at the La Brea Tar Pits and Museum,” the authors said.
“We confirm that these animals, though they were large predators that lived through tough times and are now extinct, shared common ailments with the cats and dogs in our very homes today.”
The results appear online in the journal PLoS ONE.
Citations:
H. Schmökel et al. 2023. Subchondral defects resembling osteochondrosis dissecans in joint surfaces of the extinct saber-toothed cat Smilodon fatalis and dire wolf Aenocyon dirus. PLoS ONE 18 (7): e0287656; doi: 10.1371/journal.pone.0287656
This article by Enrico de Lazaro was first published by Sci.News on 13 July 2023. Lead Image: An artist’s impression of Smilodon fatalis. Image credit: Sergio De la Rosa / CC BY-SA 3.0.
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