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The platypus has been a box of surprises since we formally “discovered” it almost 230 years ago, when the first stuffed specimen arrived in Europe and the naturalist George Shaw thought which was a hoax sewn up by some Chinese taxidermist. And let’s see, the platypus is truly unique in its species: it is a mammal that lays eggs, detects electric fields with its beak and glows under ultraviolet light. As if the above were not enough, a research team just found a surprising explanation for the color of his coat. What’s new about the platypus. The research, led by biologist Jessica Leigh Dobson from Ghent University, has identified that the platypus has melanosomes holes in their fur. What is this exactly? The organelles responsible for giving us color in our skin, hair or eyes. Until now, science assumed that hollow melanosomes existed only in birds and that those of mammals were always solid. Curiously, in birds those melanosomes are the ones that produce iridescent colors, but the platypus is dark brown, without flashes or shine. Furthermore, their melanosomes are mostly spherical, a morphology that in other animals is associated with red or orange tones, but not brown. The reason is a mystery. Why it is important. Melamine is the standard for vertebrates to provide color and protect from the sun, but what is truly key is its packaging. For decades the shape of melanosomes has served as an evolutionary fingerprint to differentiate the branches of birds and mammals. The platypus just killed it, but of course, it is so disconcerting from the beginning that it took researchers 80 years to agree on what it was, as its scientific name summarizes. The most reasonable hypothesis What this research team proposes is that the hollow melanosomes could have been an adaptation to the aquatic lifestyle of the platypus, a kind of thermal insulation mechanism in the fur for life in cold waters. But of course, if this is the case, why doesn’t the same happen with other semi-aquatic mammals? If confirmed, it would imply that this condition of hollow melanosomes evolved independently in birds and only in this mammal. The platypus continues to go on its own. Context. The platypus deserves a separate chapter in biology books: it is one of only five species of mammals that lay eggs, the monotremes. And what can we say about its appearance: it has the beak of a duck and the tail of a beaver. Although it seems harmless, it is not: it has venom like snakes and the males also have poisonous spurs on their hind legs capable of causing intense pain in humans. The icing on the cake is that the animal is capable of detecting the electric fields generated by the muscles of its prey underwater. But the platypus is different outside and inside: He is a genetic rebel. While humans have only two sex chromosomes (XX or XY), he has ten. This complexity makes their system for determining sex totally different from that of other mammals. It is, literally, one of the few animals that forces science to consider pre-established laws. How they discovered it. The discovery was almost a coincidence: Jessica Dobson was building a database of melanosomes from different mammal species when her thesis supervisor detected this platypus anomaly. The scientist passed the samples through a high-resolution microscope to examine the melanosomes inside the hairs of 12 platypus specimens taken from different parts of the body. He then extended the comparison to echidnas, marsupials such as wombats and opossums, and a hundred more mammals. No trace of hollow melanosomes, and for example their cousins, the echidnas, also lay eggs. In Xataka | The “Spanish platypus” exists and is on the verge of extinction: the very rare animal that only lives on the peninsula In Xataka | A 24-year-old platypus challenges what we knew about the longevity of the strangest mammals Cover | Dr Philip Bethge