Ancient scimitar- toothed cats had traits would lend themselves well to being group hunters that could pursue their prey to the point of exhaustion, a newly-published study on DNA extracted from a fossil found near Dawson City suggests.
By looking at the genetic makeup of the Homotherium latidens specimen, researchers at the University of Copenhagen were also able to determine that the species was likely more abundant than previously thought, and is also only very distantly related to modern-day felines.
Those findings, and others shedding light on the behaviour of the extinct big cat, are outlined in a new report published in the Current Biology science journal.
A team of researchers extracted a DNA sample from the fossil — a humerus bone found in the Klondike permafrost sediment that was so old it couldn’t be radiocarbon dated, meaning it goes at least 47,500 years back — and mapped out its entire nuclear genome.
From there, they compared it to the DNA of two species of hyena and 16 other species of cat, including the Bengal tiger, clouded leopard and domestic cat, and were able to look for specific genes that are typically related to certain traits.
The scimitar-toothed cat, which once occupied a range spanning from southern Africa to across Europe and Asia and into the Americas, has genetic characteristics that indicate it had excellent eyesight and could have been well-suited to hunting during the day.
It was also genetically adapted for endurance running with strong bones and respiratory and circulatory systems, suggesting that, rather than using its long fangs as the primary method for taking down prey, it likely chased after them instead until the soon-to-be meal collapsed from exhaustion.
“Most modern cats are crepuscular or nocturnal, but in some places perhaps due to human interference we find species active diurnally, like the cheetah,” report lead author Ross Barnett wrote in an email to the News.
“I think it just shows how marvelously adaptable and smart most cats are. They’re active whenever it’s easiest to hunt… Advantages to Homotherium have to be placed in the context of the ecosystem of the time. Yukon back then would have had bison, horses, mammoths, caribou, ground sloths, peccaries, camels, deer for Homotherium to hunt. Bison are chased to exhaustion by wolves in some places today and there is isotope evidence that bison were a food item for Yukon Homotherium.”
Adding to its hunting advantage is evidence of positive selection for genes that indicates Homotherium — not to be confused with its perhaps more well-known and larger cousins, the sabre-toothed “tigers” in the Smilodon family — could have engaged in “coordinated social interactions” that would have helped in bringing down larger prey.
Other new findings pulled from the fossil include confirmation that the species is highly genetically divergent from modern cats, branching off from them at least 22.5 million years ago. The cat whose bones were fossilized also had high genetic diversity. That, the report says, suggests that scimitar-toothed cats were actually quite abundant and had lots of other members from the same species to breed with.
The abundance of the cats was at one point believed to be low because their fossils are relatively rare finds.
“One of the things about fossilization is an animal has to die in a place that it’s likely to be fossilized, so certain types of environments just aren’t very good,” Yukon paleontologist Grant Zazula, a co-author on the report, said in an interview.
“So if you’re living in a valley bottom, the likelihood that your bones will be preserved are probably much higher than if you’re living in the mountains because there’s not a lot of sediments being deposited in a mountain-type environment to become preserved in. So it makes me kind of think that Homotherium, the scimitar cats, in the North here may have been specializing in higher altitudes … If they were living in the more mountain-y environments, more upland environments, the chances that their fossils would be preserved are quite low.”
Beyond the report’s immediate findings, Zazula said the study also helps to highlight the new opportunities that DNA and genome analysis present for paleontologists.
“Paleontology is so often stuck just studying bones and we make all these wide inferences about the shapes of bones and size of bones and the numbers of bones, so we make all these inferences about behaviour that are probably largely incorrect … But with this genetic information we can look at, it provides us this opportunity to learn about behaviour in ways that were totally impossible through regular paleontological methods.”
Mick Westbury, another co-author and a specialist in paleo-genomics, agreed, noting that advances in technology have made studying ancient DNA more easy and cost-effective than ever.
“The biggest problem with DNA from sub-fossils is that it’s normally highly contaminated by you know, all the other organisms that occupied the soil or anything that touched the bone after it was deceased, so if you could only sequence a few molecules, you would generally be stuck with those more abundant soil or fungi or whatever molecules you find,” he explained.
“But now with the new technology we can sequence millions or billions of independent DNA fragments and then we can try and fish out which ones are likely coming from an organism of interest, and that allows us to recreate the whole genome.”
While discussions of ancient DNA may conjure up images of Jurassic Park-type scenarios for some, Burnett said there are far more interesting and practical applications for genome sequencing extinct creatures.
“(People) should care because we are really moving into a fascinating time for ancient DNA work,” he wrote. “The ability to look at things that bones can’t tell you is just around the corner. Today it is population size, adaptations for diurnal hunting, and cooperative behaviour. Tomorrow it could be coat colour, or any number of cool things.”
Contact Jackie Hong at jackie.hong@yukon-news.com
