When the first duck-billed platypus specimens were sent from Australia to Europe at the end of the 18th century, the bizarre combination of mammal, bird and reptile features led many zoologists to consider them a hoax.

The reason for that first impression has now been revealed: the first analysis of its DNA code has shown that at a genetic level the platypus is indeed a unique amalgam of mammal, reptile and bird.

The platypus genome, sequenced from a female named Glennie, has allowed scientists to examine how evolution shaped not only the strange egg-laying mammal, but also relatives such as human beings. It may even offer insights into human diseases, by revealing genes that are critical to the mammalian immune system.

“This is our ticket back in time, to when all mammals laid eggs while suckling their young on milk,” said Chris Ponting, of the University of Oxford, one of the leaders of the international research team.

“The platyus genome is extremely important, because it is the missing link in our understanding of how we and other mammals first evolved.”

Francis Collins, director of the US National Human Genome Research Institute, said: “At first glance, the platypus appears as if it was the result of an evolutionary accident. But as weird as this animal looks, its genome sequence is priceless for understanding how fundamental mammalian biological processes have evolved.

“Comparisons of the platypus genome to those of other mammals will provide new insights into the history, structure and function of our own genome.”

The platypus code has already been compared with those of people, mice, dogs, opossums and chickens, as well as the draft sequence of the green anole lizard to examine its similarity to reptiles. This has shown that although it diverged from other mammals about 166 million years ago it still shares about 82 per cent of its genes with very different relatives, such as people and mice.

Other aspects of its genome, however, appear distinctly avian or reptilian in character. Ewan Birney, of the European Bioinformatics Institute, who led the genome analysis, said: “The platypus looks like a strange blend of mammalian, bird-like and reptilian features and now we know that the genome is an equally bizarre mix of all of these. It is much more of a melange than anyone expected.”

The male platypus is unique among mammals in having venomous spurs on its hind legs, with which it injects rivals and predators with painful poison. The genes that produce this venom are very similar to those found in snakes. Other reptilian characteristics include genes that support egg-laying.

The animal's sex chromosomes have similarities with those of birds. It has ten sex chromosomes, where most mammals, including humans, have only two.

Mammalian characteristics include an unexpectedly high number of genes involved in detecting scent, which is surprising because the creature spends most of its time under water with its nostrils closed.

The genetic code of the platypus, which has the Latin name Ornithorhynchus anatinus, meaning “duck-like bird-snout”, should shed light on its ability to detect prey under water using an electro-sensory organ in its bill.

The sequence, which is published in the journal Nature, shows that the platypus genome contains approximately 2.2 billion DNA letters, and about 18,500 genes. This compares with 3 billion letters and an estimated 21,500 genes in the human genome. Comparisons between the two genomes should help scientists to understand the function of genes that are critical to human health.

Mark Batzer, of Louisiana State University, said: “This is a huge genetic step. We're learning a lot about mammalian gene regulation and immune systems, which has huge implications for disease susceptibility research.”

The platypus is a monotreme, from a group of mammals that diverged from the marsupials and placental mammals about 166 million years ago.

Nature trick

— Platypus comes from the Greek for “flat foot”, reflecting its webbed feet

— The animal is native to Australia and was first described by Europeans in 1798

— When a pelt and drawing were sent to England by the Governor of New South Wales, the zoologist George Shaw was so doubtful it was real that he cut it open to look for stitches

— It is an egg-laying mammal known as a monotreme, one of only five species in the order

— On its hind legs the male has a spur that produces venom, a unique feature among mammals

Source: Times database

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