Platypus: Genetics can Explain Why They are so Strange

Platypus : Genetics can explain why they are so strange as researchers have revealed details about the evolutionary mosaic, showing that the DNA of Platypuses has parts of birds, mammals and reptiles.

Platypuses are quite strange animals. Officially they belong to mammals, animals with mammary glands, sweat glands and hair in at least one stage of life.

However, platypuses also have a robust beak, similar to that of a duck. As if it were not enough confusion, these animals still lay eggs and suck their offspring through the pores of their skin – since they have no breasts. Besides, platypuses still have some reptilian characteristics, such as claws and poisonous spurs, in addition to luminescent hair.

2008 research had already shown that these animals’ DNA contained parts of birds, mammals and reptiles. However, a January 6 study, available from Nature, showed how this evolutionary mosaic might have happened.

The genome of several animals already has complete genetic maps, including humans. Now, we have the first genomic map of platypus and echidnas – another Australian mammal also lays eggs and is just as strange as the one already mentioned. Genetic analyzes have shown that platypuses are the only animals in the world to have ten sex chromosomes. The echidnas are nine and we humans are only two.

Despite all these bizarrities, the researchers were able to trace a relationship between the shape of the platypus chromosomes and humans, which may provide a missing link in human evolution.

Why are platypuses so strange, anyway?

Within the mammalian class there are three other subclasses: placentals, which have the placenta – an organ that makes gas exchanges between the fetus and the mother – as the name says; marsupials, such as kangaroos and skunks that have an atrophied placenta and therefore need to end the puppies’ development in a pouch; and, finally, monotremes, to which our strange platypus and echidna belong. As said before, this last group lays eggs and feeds their young with milk after they hatch. The study in question even showed that platypuses lost the genes that form nutrients in eggs. This is precise because the puppies receive milk from the mother after birth.


Research has shown that monotremes have a different gene configuration. The part is inherited from mammals, but other elements come from birds and reptiles. Analyzes also showed individual evolutionary differences between the monotremes and the two other classes of mammals. Genes for the production of haptoglobin, lactation and chemical sensory receptors were shown to be quite different genetically in platypuses, for example.

Sex chromosomes showed that monotremes had an ancestor with those same chromosomes in the form of a ring. Over time, this arrangement has changed and may have given rise to the most common structures today: XX for females and XY for males. In general, the researchers could see that platypuses have more similarities to ducks than to most mammals.