I Have Your Transitional Species Right Here

When the British naturalist George Shaw first saw the platypus in 1799 he thought it was a hoax.

Now a team of scientists has finally determined the platypus’s entire genetic code and its DNA is as odd as the animal’s exterior bearing genetic modules that are in turn mammalian, reptilian and avian.

The animal’s reptilian roots provide the genes for egg laying and for making snake venom (which the animal stores in its legs) but its mammalian genes provide for making milk (despite not having nipples).

Then there are the ten sex-determining chromosomes that scientists still don’t know what to make of. Most mammals have two sex chromosomes, X and Y but not only do platypuses have 10 instead of two, but some of those resemble the Z and W chromosomes of birds.

“It’s such a wacky organism,” said Richard Wilson, director of the genome center at Washington University in St. Louis, who led the two-year international effort, described online Wednesday in the journal Nature.

Yet in its wackiness, Wilson said, the platypus genome offers an unprecedented glimpse of how evolution made its first stabs at producing mammals. It tells the tale of how early mammals learned to nurse their young; how they matched poisonous snakes at their own venomous game; and how they struggled to build a system of fertilization and gestation that would give rise to the first humans.

Update: There is a very informative video here from the journal Nature about this new finding.