Published online 28 January 1999 | Nature | doi:10.1038/news990128-5

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The smilodon's smile

Did the sabre-toothed tiger grin like the Cheshire Cat in Alice in Wonderland? Or was he more of a pursed-lips kind of pussycat? This conundrum - or more precisely, that of how the heads of now-extinct cats looked and how this influenced their behaviour - has been a bone of contention among palaeontologists.

In the thirties, the accepted wisdom was that apart from their long canine teeth, sabre-toothed cats such as the American Smilodon - whose remains dominate the feline fossil record - looked roughly similar to the cats of today. But since the late sixties the prevailing view has been that Smilodon had more of a dog-like face, with long, jowl-like lips, a flattened 'snout', a retroussé ┬«ose and low-set ears. The long lip-line would have allowed the animal a gape wider than that seen in modern cats, so it could have used its sabres more effectively. The short nose was simply a reflection of the small nasal bones of the Smilodon skull.

Now Alan Turner of Liverpool John Moores University, UK, and colleagues are challenging this view. They report in the Zoological Journal of the Linnean Society that their measurements, together with studies on fossil and living cats, indicate that the earlier restorations were correct after all, returning a more feline smile to the face of Smilodon.

Turner and colleagues believe, for example, that the feeding behaviour of modern carnivores does not support previous assertions that Smilodon 's extended sword-shaped canines would have hindered their eating. Modern cats, they argue, do not open their mouths wide enough to make a sizeable gap between the tips of their upper and lower canines - a feature hitherto deemed essential for meat eating by many previous theorists - but instead are able to 'grin'. That is, they have highly elastic lips that can be pulled back to bare the teeth necessary for food shearing. Thus the researchers feel that the corners of Smilodon 's mouth were actually quite close together, like those of its modern day descendants. There was no need for Smilodon to have had an unusually long lip-line to have used its sabres effectively, or to ingest food through the side of its mouth as well as from the front.

The team goes on to reason that this ability to retract the upper lip and nose - to which skull development also points - has a bearing on the kind of nose the sabretooths might have had. It would, they suggest "obviate the need to evolve a retracted nose," - if their analysis of the nasal bone-to-nose-position ratios of modern cats is anything to go by.

"The results of our studies clearly point to a broadly feline appearance for the head of Smilodon," the group concludes. Although they concede that without knowing what its facial markings and whiskers were like, "the final character" remains elusive.