Native to eastern Australia, the duckbilled platypus is regarded as a mammal. Yet it lays eggs like a bird. However, it nurses its young like a mammal, on milk.

The male platypus also has a poison spur on its hind leg, which is more characteristic of reptiles.

And now that it has been mapped, the genome of the duck-billed platypus turns out to be as mixed as the traits of the animal itself.

Said researcher Mark Batzer of Louisiana State University,

"One big surprise was the patchwork nature of the genome with avian, reptilian and mammalian features".

Of particular interest was the genes for of the male's poison spur:

Scientists were also eager to find out how venom production became a part of the platypus genome. When researchers began analyzing the genetic sequences responsible for venom production in the male platypus, they made a surprising finding. They discovered that venom produced by the male platypus arose from duplications in certain genes over the course of evolutionary time that had been passed on from ancestral reptile genomes. The reptilian lineage displays a similar duplication of venom genes, but that duplication appears to have occurred independently during the evolution of reptiles, giving them similar powers to produce venom.

- "Duck-Billed Platypus Genome Sequence Published", National Institutes of Health (May 7, 2008)

The platypus is one of the few survivors of a classification of mammals called monotremes, found only in Australia and New Guinea today.

It is best known for its electrosensitive bill, which it uses to locate things under water, because it keeps its eyes shut when submerged.