Newly identified American saber-toothed cat species was larger than a tiger and hunted rhinos

A saber-toothed cat, larger than the biggest tigers alive today, lived in North America between 5 - 9 million years ago, and used its massive forearms for hunting prey such as bison and rhinoceros, researchers have said.

The previously unknown species is believed to be one of the largest cats which has ever lived, and was identified several years after a large upper arm bone specimen labelled as that of a cat was found in the collection of the University of Oregon Museum of Natural and Cultural History, but which had mystified scientists.

The huge bone was rediscovered by John Orcutt, assistant professor of biology at Gonzaga University, when he was a graduate student, and the find sparked a years-long effort to find out what species of cat it could be from.

In all, the researchers used seven previously uncategorised fossil specimens along with other fossils and bone samples from around the world to describe the new species.

The cat is an ancient relative of one of the best-known prehistoric animals - the saber-toothed cat Smilodon, although it would have been far larger and more fearsome.

It would have weighed up to 900 pounds (64 stone, or 408kg), and “could have managed to kill prey weighing up to 6,000 pounds (2.7 tonnes). In comparison, a large adult male tiger will weigh up to 700 pounds (310kg).

“We believe these were animals that were routinely taking down bison-sized animals,” said study co-author Jonathan Calede, an assistant professor of evolution, ecology and organismal biology at Ohio State University.

“This was by far the largest cat alive at that time,” he said.

The specimen which Dr Orcutt rediscovered was originally excavated on the traditional lands of the Cayuse, a tribe joined with the Umatilla and Walla Walla in the Confederated Tribes of the Umatilla Indian Reservation.

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In recognition of the specimen’s origin, the research team collaborated with the Tamástslikt Cultural Institute to name the new species Machairodus lahayishupup. Machairodus is a genus of large saber-toothed cats which lived in Africa, Eurasia and North America, and in the Old Cayuse language, Laháyis Húpup means “ancient wild cat”.

But the research not only revealed the previously unrecognised species, it also provides important new insights as to how cats’ leg bones can indicate which species they belong to.

"One of the big stories of all of this is that we ended up uncovering specimen after specimen of this giant cat in museums in western North America," Dr Orcutt said.

“They were clearly big cats. We started with a few assumptions based on their age, in the 5.5 to 9 million-year-old range, and based on their size, because these things were huge.

“What we didn’t have then, that we have now, is the test of whether the size and anatomy of those bones tells us anything - and it turns out that yes, they do.”

The largest of the seven Machairodus lahayishupup humerus fossils available for the analysis was more than 18 inches (45cm) long and 1.7 inches in diameter. In comparison, the average modern adult male lion’s humerus is about 13 inches long.

The researchers hypothesised that if a single forearm bone could be useful in telling species apart, that would still be true among the big cat species alive today.

Dr Calede and Dr Orcutt visited numerous museums in the US, Canada and France to photograph forearm specimens of lions, pumas, panthers, jaguars and tigers, as well as fossils of previously identified extinct big cats.

Dr Calede used software to place landmark points on each digitised sample that, when drawn together, would create a model of each elbow.

“We found we could quantify the differences on a fairly fine scale,” Dr Calede said. “This told us we could use the elbow shape to tell apart species of modern big cats.

“Then we took the tool to the fossil record - these giant elbows scattered in museums all had a characteristic in common. This told us they all belonged to the same species.

“Their unique shape and size told us they were also very different from everything that is already known. In other words, these bones belong to one species and that species is a new species.”

The researchers calculated estimates of the new species’ body size based on the association between humerus size and body mass in modern big cats, and speculated about the cat’s prey based on its size and animals known to have lived in the region at that time.

They said rhinoceros were particularly abundant, as well as ancient species such as the giant camels of the High Arctic, which roamed what is Canada until around 12,000 years ago, and giant ground sloths which were as large as modern elephants.

One specimen included teeth from the lower part of the jaw, but it did not include the saber-shaped canines.

“We’re quite confident it’s a saber-toothed cat and we’re quite confident it’s a new species of the Machairodus genus,” Dr Orcutt said.

“The problem is, in part because we haven’t necessarily had a clear image in the past of how many species were out there, our understanding of how all these saber-toothed cats are related to each other is a little fuzzy, particularly early in their evolution.”

Establishing that the humerus alone can be analysed to identify a fossil cat has important implications for the field, the researchers said. Not least because saber-toothed cats’ large forearm bones are the most common specimens of fossil cats found in excavations.

Only a reconstruction of the evolutionary history of saber-toothed cats can determine where this new species fits in, but Dr Orcutt and Dr Calede believe Machairodus lahayishupup existed early in the evolution of the group.

A discovery that this giant cat in North America existed at the same time similar animals lived around the world also raises another evolutionary question, Dr Calede said.

“It’s been known that there were giant cats in Europe, Asia and Africa, and now we have our own giant saber-toothed cat in North America during this period as well,” he said.

“There’s a very interesting pattern of either repeated independent evolution on every continent of this giant body size in what remains a pretty hyperspecialised way of hunting, or we have this ancestral giant saber-toothed cat that dispersed to all of those continents.

“It’s an interesting paleontological question.”

The research is published in the Journal of Mammalian Evolution.