Sabre-tooths and tabbies part of the same close-knit family

One curls up in your lap with a comforting purr, the other prowled the prairies of North America before the onset of the last Ice Age.

Whether it is the fearsome sabre-toothed tiger of prehistoric times, the graceful cheetah or the domestic tabby, a DNA study has shown that cats are a tight-knit group of animals.

The latest research into the genetic relationship between the cats - living and extinct - has confirmed the common ancestry of some of the most terrifying yet beautiful predators on earth.

Within the space of 15 million years - less than a quarter of the time since mammals rose to prominence after the demise of the dinosaurs - the cat family evolved to become the supreme land predators.

Unravelling the complex family tree of cats has traditionally relied on the skills of zoologists and palaeontologists - scientists trained to make judgments based on the shape, structure and age of bones.

In recent years a new tool has emerged based on the analysis of a special kind of DNA found in tiny cellular structures called mitochondria, the only DNA found outside the cell's nucleus.

A team of scientists from Britain, the United States, Canada, Sweden and Australia used mitochondrial DNA from the blood of living cats and the bones of dead ones to update the Felidae family tree.

Their conclusions broadly support many of the judgments from earlier studies, but the scientists have also made some fascinating insights into how some cat species came into existence.

It was thought, for instance, that cheetahs may have evolved in the New World and later moved to the Old World, where they gave rise to the cheetahs alive today.

"There has been a lot of to-ing and fro-ing of animals across the land bridge separating North America and Asia at the Bering Strait and cats were no exception," said Ross Barnett of Oxford University's Henry Wellcome Ancient Biomolecules Centre.

But when the scientists analysed the mitochondrial DNA of the American "cheetah", a species called Miracinonyx trumani, they found that its closest relative was not the African cheetah but the American mountain lion or puma, Puma concolor.

"The data suggests that cheetahs originated in the Old World and that a puma-like cat then invaded North America around six million years ago," Mr Barnett said.

Mitochondrial DNA taken from the bones of a museum specimen of Miracinonyx not only suggests that its closest relative is the American puma, but that they both shared a common ancestor as recently as three million years ago - half the age of the Old World cheetah.

The difficulty with understanding the true origin of the American "cheetah" is that it had evolved to look similar to the true Old World cheetah because of what is known as convergent evolution - unrelated animals coming to look the same because they occupy the same ecological niche.

In this case both species of cat had exceptionally long legs, wide nostrils to supercharge their lungs with oxygen and other adaptations for a high-speed chase.

But both sets of traits had evolved independently on separate continents.

And what about the domestic cat? The present study does not assess the moggy's position in the wider cat family, but a study last year showed that man and cat have been close friends for at least 9500 years.

Archaeologists working in Cyprus found a skeleton of a wild cat - a species introduced to the Mediterranean island by man - carefully buried next to a human grave.

This first proven association between man and cat predates the supposed domestication of cats in Egypt by 4000 years. The rest is feline history.

Secrets of cats

* New DNA research has confirmed that cats, from the domestic kind to ferocious wild predators, are a tight-knit group.

* Humans and cats have been close friends for at least 9500 years.

* Sabre-tooth cats, which disappeared about 13,000 years ago, diverged early on from the ancestors of modern cats and are not closely related to any living feline species.

- INDEPENDENT