Elephants have been revealed to have the most sophisticated sense of smell in a league table of mammals compiled by scientists.

Researchers who examined olfactory receptors, the proteins involved in detecting smell, found that African elephants had almost 2,000 olfactory genes - more than twice that of dogs and five times more than human beings.

The findings back up research which has shown that elephants have a more sensitive sense of smell than bloodhounds and can detect water several miles away.

The authors of the study, published in Genome Research, examined 13 mammalian species. They said the human sense of smell may have diminished as our eyesight grew more sophisticated.

"The functions of these genes are not well known, but they are likely important for the living environment of African elephants," said Yoshihito Niimura, author of the report

"Apparently, an elephant's nose is not only long but also superior."