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How a Smilodon sabretooth cat closed its gaping mouth
By Victoria Gill
Science and nature reporter, BBC News

Animation of smilodon from the BBC series, Walking With Beasts
The sabretoothed cats killed prey with a deep stabbing bite to the throat

The mystery of how prehistoric sabretoothed cats coped with their oversized teeth has been solved in part by a new analysis of the cats' jaws.

To impale prey with these impressive weapons, the famous sabretoothed cats must have opened their mouths wider than any modern big cat, but it was unclear if their jaw muscles were strong enough to do it.

Now the new analysis reveals that the cats' jaw muscles evolved into a specialised pattern, which allowed them to open their mouths so wide.

Details are reported in the Zoological Journal of the Linnean Society.

Weak bite?

Per Christiansen, from Aalborg University in Denmark, led the study. He took a novel approach to studying the extinct predators by creating a complex model of how their jaws moved.

They delivered a quick, powerful and deep stabbing bite to the throat or upper neck of their prey
Per Christiansen
Aalborg University in Denmark

Beautifully preserved skeletons of the most recently extinct sabretoothed cat, Smilodon, have been uncovered in tar pits in the US, offering the researcher plenty of fossilised remains to work with.

These fearsome-looking cats - the biggest of which would have hunted very large prey, including buffaloes, horses and extinct giant ground sloths - had a relatively weak bite force compared to their modern feline relatives, previous studies have revealed.

But this is not surprising, according to Dr Christiansen. He has found the cats must have had remarkable jaw muscles to close their mouths with any force at all.

"Smilodon could open its mouth wider than any modern cat," explained Dr Christiansen, "because if you have big teeth, you have to open your mouth at a very high angle to get anything in your mouth."

Fatal stabs

Lion skull (left) next to a Smilodon skull
Smilodon (right) was able to open its mouth wider than any modern cat

Over the years, scientists have debated what the now extinct cats used their enormous teeth for, with some even suggesting the teeth were ornaments that males used to attract mates.

But the consensus is now that the teeth, which measured up to 20cm, delivered final, fatal stabs to already subdued prey.

Bulkier and more muscular than most modern cats, Smilodon would have brought large animals down with its forelimbs.

"They pounced on their prey, wrestled it to the ground and twisted the neck with massive forelimbs," explained Dr Christiansen.

"They then delivered a quick, powerful and deep stabbing bite to the throat or upper neck. But, there were no minute-long massive asphyxiating throat-clamps like those used by modern big cats when they suffocate prey. The sabrecats simply didn't have the jaw muscles for that."

Opening their mouths sufficiently wide to kill and consume their hard-earned meal would have stretched and significantly weakened their jaw muscles.

The cat species became gradually more and more specialised, culminating with monsters such as Smilodon
Per Christiansen

Dr Christiansen created a model of the cats' jaws, carefully calculating how they must have moved, to work out how Smilodon evolved to compensate for this weakness.

His model revealed how the cats' jaw muscles were aligned to pull its jaws closed, very directly and efficiently.

But Smilodon would also have done something that every cat-owner can see a relic of in their own pet.

"When you put a piece of food on the floor for your cat, you'll see it bobs its head forward as it eats it," he explained.

"And we know that [Smilodon] probably closed its jaws by twisting its head downward and throwing its head forward.

"Its neck was longer than that of modern cats and its neck muscles would have been stronger."

'Killing ecology'

The study also looked back at the earliest and most primitive sabretoothed animals.

"Smilodon was outrageous in terms of its anatomy," said Dr Christiansen.

"It was the most [highly evolved and therefore] different from modern cats, so to understand this animal from a biological sense, you need to study more primitive animals to work out why they have become that way through evolution."

Artist's impression of smilodon hunting (Image: Science Photo Library)
Smilodon would have brought down prey with its powerful forelimbs

He examined hundreds of skulls, drawing an evolutionary map showing why sabretooths evolved such different jaw anatomy from modern cats.

"Killing ecology", he explained, was the driving factor - the evolutionary pressure to kill prey with a deep and efficient stab to the throat.

"The cat species became gradually more and more specialised, culminating with monsters such as Smilodon," said Dr Christiansen.

As sabretooths evolved longer canine teeth, their jaw muscles actually grew smaller, but the fibres became more vertically orientated and thus probably more efficient in closing the jaw.

SOURCES

Dr Christiansen explained: "At the same time, changes in the way the muscle fibres inserted on the lower jaw meant that the animals could stretch their muscles more - the fibres became re-orientated so as to allow a higher gape, necessary for gaping with huge fangs."

But their impressive appearance might well have been key to their demise; the sabre-toothed cats were dependent on large, relatively slow-moving prey.

"They had very powerful but heavy bodies and rather short, extremely powerful legs," said Dr Christiansen, "so they probably weren't very fast, and certainly nowhere near as fast and agile as leopard and tigers."



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