Whether waking up to a slobber-soaked ribbon draped across one's face or an unfortunately massacred mouse 'gifted' in one's slippers, anyone intimate with a cat can attest that their tiny tiger is evolutionarily built to hunt.
The domestic cat's distantly related predecessor, which split from the ancestors of tigers and modern cats 20 million years ago, was an exponentially more fearsome felid.
Weighing up to 600 pounds (270 kilograms), Smilodon fatalis was part 'cat,' part cruise missile: an ambush hunter with scimitar teeth.
In fact, its Greek-Latin name means something like "deadly knife-tooth," on account of the frightening murder-fangs fastened to its jaws.
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Yet in a recent study published in Frontiers in Veterinary Science, researchers found evidence that this powerful predator may have become inbred and developed spinal malformations before it exited the evolutionary stage at the end of the last Ice Age, circa 12,000 years ago.
The researchers used optical methods and computed tomography (CT) scans to examine more than 3,700 vertebrae – comprising at least 849 individual S. fatalis individuals – looking for signs of trauma, disease, and genetic defects.
These animals died and had their skeletal remnants preserved in the La Brea Tar Pits of Los Angeles, which may be the "world's richest ice age fossil site."
Such tar pits have become pop-media favorites, featured in iconic series like The Flintstones, The Simpsons, and a perhaps un-iconic 20th-century slapstick comedy starring former Beatles' drummer Ringo Starr as a 'caveman.'
Tar pits were also very deadly.
"The tar seeps were a carnivore trap," the researchers explain. "A large herbivore that became mired in the asphalt inadvertently would attract large carnivores and scavengers, which would themselves become entrapped in great numbers."
The S. fatalis vertebrae revealed diverse, sometimes severe pathologies, including many hints of chronic inflammatory disease. Additionally, they exhibited over 200 congenital vertebral malformations and nearly 50 fused vertebrae, as well as signs of abnormal bone growths and skeletal breakdown.
The researchers also identified lumbar vertebrae (from the lower back between the ribcage and pelvis) from three different individuals with signs of spinal nerve tumors (SNTs), which may result from genetic mutations.
Three may not sound like much.
But relative to the specimens examined in this work, the researchers estimate an SNT prevalence of 353 per 100,000 individuals. This is much higher than the upper-range estimates of incidence in humans, which is only 0.38 per 100,000 persons, the researchers note.
The consequences of these congenital malformations could have been catastrophic for a population facing decline.
For comparison, most humans with SNTs report pain. In dogs, these tumors also often cause pain, along with muscle wasting and lameness, factors that would have significantly affected an ancient animal's hunting abilities.
Perhaps this is why we see so many hundreds of the Smilodon specimens in the tar pits.
An animal battling declines in function and disabilities may have licked its chops (and ditched some of its discretion) at the sight of a huge, juicy herbivore struggling to extricate itself from black, bubbling baths of tar.
Though well-supported by physical evidence, the inbreeding scenario may be impossible to prove without DNA analysis. And, unfortunately, "as is the case with all fossils from the LBTPM, no soft tissues are preserved," the researchers note.
Still, this presents worrying modern-day consequences as animal populations are under the multifold threats of climate change, environmental encroachment, and habitat loss.
Related: There's One Predator That Terrifies Bears And Mountain Lions Alike
"There is evidence that due to dramatically declining population numbers, there was an increasing occurrence of inbreeding in mammals at the end of the Pleistocene, with different health consequences," the researchers conclude, explaining that this issue was not exclusive to S. fatalis:
"DNA analysis of mammoths found in the permafrost revealed a high degree of inbreeding before they became extinct, potentially causing serious diseases such as diabetes mellitus and sensory deficits."
This research was published in Frontiers in Veterinary Science.
This article was fact-checked by Rachel Garner and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.