Scientists worked together to draw up the first blueprint of the platypus genetic code.

Published yesterday in the journal Nature, it shines a light on the early history of mammals, when furry animals had reptilian features.

The duck-billed platypus, a native of Australia, is classified as a mammal because it produces milk and has a coat of fur.

Venom

But the platypus also lays eggs - one of only two mammals, known as monotremes, to do so.

It also sports a duck-like bill equipped with a sophisticated electrosensory system used to forage for food underwater, and males possess a pair of hind leg spurs that can deliver a powerful venom.

The new genome sequence was constructed from DNA taken from a female platypus named Glennie, collected from a river at Glenrock Station, New South Wales, Australia.
When European experts first laid eyes on a duck-billed platypus sent from Australia in the 19th century, they assumed it was a hoax.

In fact the platypus had been following its own peculiar evolutionary path since diverging from the rest of the mammalian lineage 166 million years ago.
Analysis of the creature's genome - its complete genetic "code book" - revealed that the platypus shares 82% of its genes with humans, mice, dogs, opossums and chickens.

Genes were found both for egg-laying, a feature of reptiles and birds, and producing milk, a distinctly mammalian characteristic. Although the platypus lacks nipples, its young suckle milk through the creature's abdominal skin.

The genes involved in generating the spur venom were strikingly similar to those belonging to poisonous snakes and lizards. Both were from the same gene family, but they evolved independently.

Evolution

Some of the platypus's curious attributes are solely its own, such as the sensors in its bill which pick up weak electric fields emitted by underwater prey.

Senior scientist Dr Richard Wilson, director of The Genome Center at Washington University in St Louis, US, said: "The fascinating mix of features in the platypus genome provides many clues to the function and evolution of all mammalian genomes.

"By comparing the platypus genome to other mammalian genomes, we'll be able to study genes that have been conserved throughout evolution."