The Venomous, Egg-Laying, Duck-billed Platypus

This odd Australian mammal looks like a duck wearing a fur coat. Many other descriptions could be – and have been – made. People from the northern hemisphere might say it looks like a beaver trick-or-treating with a clumsily stuck-on fake duck bill.

Famous also for laying eggs, the playtpus flummoxed clever men back in 1799 when the first dead and preserved one was brought to Europe. They confidently pronounced it a fake, made of several animals sewn together.

Mammal-like reptiles diverged from the lineage they shared with birds and reptiles about 280 million years ago. Around 80 million years later, the monotremes—or egg-laying mammals—split off from the mammalian lineage, says Rebecca Young, a biologist at the University of Texas at Austin. All that remains of that branch of the family tree is the platypus and four species of echidna.

This split happened before the evolution of the placenta, so in that sense they are somewhere between a lizard and a placental mammal retaining some reptilian and mammalian features, according to Young.

Although the platypus lays eggs, unlike a mammal, like a mammal it suckles its young on milk, but the platypus’ milk seeps through pores in its abdomen, not through teats as in all other mammals. Another incredible adaptation is how they forage for food. Platypuses close their eyes, ears, and noses underwater and find prey by sensing electric currents with their duck-like bills. These bottom feeders scoop up insects, larvae, shellfish, and worms in their bill along with bits of gravel and mud. Platypuses do not have teeth, so the bits of gravel help them to “chew” their meal.

They also very unusually for mammals, and more like their reptilian ancestors have venom! And their venom is located in a spur in the males’ heels—a unique method of delivery among venomous creatures. Platypus venom contains genes that resemble the venom genes of other animals, including snakes, starfish, and spiders. It’s real venom, with 83 toxins and is likely an example of convergent evolution, in which unrelated species evolve similar traits.

We will learn more about platypus evolution as time and research goes on. The elements of mutations and adaptations and randomness determine how we acquire things over time, and it’s fascinating to try and work out the puzzle, like scientific detectives.



Thanks Liz LangleyNational Geographic

Wes Warren of the Washington University School of Medicine in St. Louis led the 2008 study that found that the platypus has a “fascinating combination of reptilian and mammalian characters.”

Related: “Platypus Genome Reveals Secrets of Mammalian Evolution

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