The platypus ( Ornithorhynchus anatinus ) is an animal native to Western Australia and the island of Tasmania. In addition, they have the appearance of a beaver and have a duck’s bill. These curious animals have the scientific community puzzled due to their peculiarities: they lay eggs instead of giving birth, they produce milk and, as if that were not enough, the males have poisonous spurs. Likewise, they have many more sex chromosomes than other mammals, which is why they are considered one of the rarest animals on the planet.
Why do platypus produce milk?
According to a study carried out by the University of Copenhagen (whose results have been published in the journal Nature ) platypuses are mammals, although they retain many characteristics of their ancestors.
To understand the evolution of platypus, it is necessary to go back to the ancestors of mammals, that is, the first synapsids. These broke away from their sister group (the sauropsids) around 300 million years ago. Sauropsids gave rise to today’s dinosaurs, birds, and reptiles, while synapsids continued to evolve for about 200 million years. Thus, the first mammals on record appeared, including australosphenids, close relatives of platypus and echidnas (monotreme and insectivorous mammals, with small heads and sharp snouts).
However, to find out how they have survived to this day and what genetic peculiarities they present, the researchers had to decode the platypus genome. In this way, as researcher Guojie Zhang from the University of Copenhagen argues, they were also able to investigate how mammals, including humans, evolved.
One of the rarities of platypuses is that they can lay eggs and at the same time suckle their young, something that seems completely incompatible with each other. In addition, the milk they produce does not come from the mammary glands, but they expel it directly through the pores of the skin. The answer to this question, according to the research, is found in the three genes for vitoligenin, an essential protein for egg formation. These three genes are present in birds, but not in humans.
The scientists discovered that platypus still retain one of these three genes, which is why they continue to lay eggs even though they no longer need that protein for their young to develop normally. In fact, in all mammals, vitellogenin has been replaced by casein, a protein that is quite present in breast milk. Thus, a team of researchers was also able to discover that platypus’ milk is quite similar to that of other mammals, such as humans, cows or goats.
