The bones of three saber-toothed tigers reveal rare spinal column abnormalities. These lesions are consistent with the presence of spinal nerve tumors, although they do not allow a definite diagnosis. They offer a new clue to the fragility of Smilodon fatalis – its scientific name – before its extinction.
The fossils come from the La Brea tar pits in California. This site has preserved several thousand bones of Pleistocene predators. Researchers thus have an exceptional set to compare the diseases and malformations that appeared in these animals.
Skull of Smilodon populator Lund, 1842, exhibited at the Museu de Zoologia da Universidade de São Paulo.
Image Wikimedia
The team examined 849 sacral bones (sacrum), 2,130 lumbar vertebrae, and 743 cervical vertebrae. Three specimens showed a characteristic enlargement of the openings through which the spinal nerves pass. This shape is consistent with a spinal nerve tumor, even though the soft tissues have disappeared.
The estimated frequency reaches 353 cases per 100,000 individuals in the studied sample. This figure cannot be directly compared to medical statistics: the fossils come from a particular assemblage, influenced by preservation conditions and by the functioning of La Brea's natural traps.
These presumed tumors could have caused pain, limb weakness, or difficulty moving. For a large predator, such problems could reduce the ability to pursue prey.
The photograph of a fossil vertebra, referenced HC 12233, is shown on the left. An 8-millimeter anomaly is highlighted by an arrow and blue marks.
On the right, a black-and-white anatomical drawing represents the same vertebra, with the anomaly colored in black.
Reference: Namura et al., 2013, type IIc.
Researchers consider a link with inbreeding. When the number of individuals decreases, animals have fewer partners and crossbreeding between relatives becomes more frequent. Certain unfavorable mutations can then become more common in the population.
This interpretation, however, remains a hypothesis. The DNA of the studied animals is not available to directly measure their genetic diversity. The anomalies could also result from other factors, and the La Brea sample does not necessarily represent the entire species.
Smilodon fatalis disappeared from North America about 12,000 years ago. The new data show how possible diseases and genetic weakening can accompany the decline of an animal population.