One of Ancient America’s most distinctive predators — the saber-toothed cat — likely wasn’t native to the continent, as had been thought for decades.
Instead, according to a team of paleontologists, the surprising variety of big cats that thrived in North America over the millennia can only be the result of waves of sabertooth immigrants from other parts of the world.
Indeed, a remarkable diversity of the great cats prowled America for millions of years, until the last of them vanished about 11,000 years ago.
But their origins — and what links they might have shared with sabertooths in Europe and Asia — have been debated for more than a century.
To distinguish among them, scientists often study the skulls, specifically the teeth and jaws, to discern how different species went about the business of killing.
Some ancient American cats were the familiar sabertooths, highly specialized hunters with giant canine teeth that killed prey not with a single stabbing blow, but through the massive blood loss that followed a well-placed bite to the neck.
Among the cats that used this tactic was a species known to scientists for decades as Nimravides catocopis, a tiger-sized predator that lived about 9 million years ago, and whose bones were first discovered in Kansas in the 1880s.
(Learn about a more recent fossil found nearby: “15,500-Year-Old Mammoth Bones and Hunting Tools Found ‘Close Together’ in Kansas“)
But sabertooths like N. catocopis weren’t true felines.
That title went to more “primitive,” less specialized species with smaller, cone-shaped teeth like the cats we know today.
These predators felled their prey by suffocating with a prolonged bite to the neck, a method that’s trickier and riskier to execute.
Since the earliest fossils of cats found in North America are all feline-like, lacking saber teeth, many scientists have assumed that sabertooths like N. catocopis were native to the New World, having evolved from an early feline that migrated from Europe more than 15 million years ago.
By this logic, both American and European sabertooths would have evolved separately over time to arrive at the very same trait — distinctive elongated teeth — a phenomenon known as convergent evolution.
But a new analysis of skulls from the U.S. and Europe refute this idea, said Manuel Salesa, paleontologist at the National Museum of Natural Sciences in Madrid, Spain.
“For many years some paleontologists have defended the hypothesis that M. catocopis and most of the North American primitive saber-toothed cats were a part of a native American lineage originating from a feline immigrant,” he said in an interview.
“Nevertheless, the similarities between these North American cats and the Old World species are too extensive to be the result of convergent evolution.”
Instead, he said, the traits that the specimens share are better explained by the immigration of saber-toothed cats to North America in several surges over relatively recent geologic time.
Salesa and his colleagues published their findings in the Journal of Vertebrate Paleontology.
The team, coordinated by paleontologist and paleoartist Mauricio Antón, surveyed a variety of saber-toothed specimens from the U.S., including the fossil of N. catocopis and a more recently discovered species unearthed in Colorado, originally named Machairodus coloradensis.
While both are considered true sabertooths, N. catocopis has the more “primitive” feline-like features, including smaller canines, suggesting it was less specialized for the sabertooth’s trademark killing bite, Antón said.
The Colorado cat, however, was more derived and formidable, standing more than a meter high at the shoulder and having more pronounced knife-like teeth.
This suggests the species was more specialized, and higher up the sabertooth family tree.
In comparing these specimens to their European contemporaries, Salesa said, the team found “extensive” similarities between the Kansas cat N. catocopis and a cat found in Spain known as Machairodus aphanistus.
“Basically, Machairodus aphanistus and N. catocopis, although having serrated and flattened upper canines, retained a primitive morphology in the mandible (jaw) and skull, resembling those of the felines,” he said.
And at the same time, the more developed Colorado cat bore equally striking likenesses to Amphimachairodus giganteus, a large, scimitar-toothed cat whose range covered much of Europe and Asia.
These two species shared the same “set of mandible and skull modifications necessary to refine the killing technique employed by saber-toothed cats,” Antón noted.
Ultimately, the team concludes that these and other traits are so similar that the American cats should be reclassified under the genera of their European cousins, making Nimravides catocopis now Machairodus catocopis, while Machairodus coloradensis would become Amphimachairodus coloradensis.
Moreover, the diversity of the American cats could be explained by an equally diverse series of immigration events over time, the scientists suggest.
In this scenario, an animal like M. aphanistus loped across the Bering land bridge some 9.5 million years ago, and its descendants eventually included the M. catocopis that was discovered in Kansas.
Similarly, a separate more recent wave likely took place about 7 million years ago, Silesa added, “when the Old World Amphimachairodus lineage reached North America and gave origin to A. coloradensis.”
Adding to their case, the researchers point out that other generally accepted animal migrations took place at around the same times, and by the same routes, including the journey of the primordial horse Hipparion from America to Asia.
In the end, Salesa and Antón note that these “evolutionary comings-and-goings” only describe the lineages of two species of North American sabertooths.
Several other species hunted Ancient America for millions of years before and after them. It was only relatively recently, for example, that the famous Smilodon, best known from the Rancho la Brea Tar Pits, made its appearance.
“Such diversity of saber-toothed cat species … can only mean one thing: These animals had developed an unusually successful way to hunt their prey. Such a realization only makes it more mysterious that they vanished completely at the end of the Pleistocene, ‘only’ 11,000 years ago,” they said.
Mauricio Antón, Manuel J. Salesa, & Gema Siliceo (2013). Machairodont adaptations and affinities of the Holarctic late Miocene homotherin Machairodus(Mammalia, Carnivora, Felidae): the case of Machairodus catocopis Cope, 1887 Journal of Vertebrate Paleontology DOI: 10.1080/02724634.2013.760468