#1022 Why is a duck-billed platypus so odd?

Why is a duck-billed platypus so odd? It has a beak, no teeth, lays eggs, sweats milk, has 10 sex chromosomes, has webbed feet, has fur that glows, they have no stomachs, and has venomous spurs.

The duck-billed platypus is native to Australia. Its name comes from Greek and means “flat foot”. It is so bizarre that when it was discovered by Europeans, they didn’t believe it was real and thought that someone had sewn bits of other animals together. The duck-billed platypus is classed as a mammal, which is where all the confusion comes from. Mammals are defined as warm-blooded vertebrates that have fur, secrete milk for their young, and give birth to live young. Duck-billed platypuses lay eggs rather than give birth to live young. However, they are not the only mammals that do this. There are five mammals that lay eggs. They are the duck-billed platypus and four different species of echidna. The duck-billed platypus is a mammal, but it appears to be a mix of mammal, bird, and reptile. Let’s have a look at all of its interesting characteristics.

The bill first. It is called the “duck-billed” platypus, but its bill is not the same as a duck’s. A duck’s beak is made up of two protruding pieces of bone, covered in keratin. Keratin is the material our fingernails are made of and it makes duck’s beaks very hard. The duck-billed platypuses’ beak is also made of bone, but it is covered in thin, soft skin. Both ducks and duck-billed platypuses use their beaks to dig through the mud at the sides and bottom of ponds and rivers, but duck-billed platypuses also use theirs for electrolocation. This is something that sharks do as well and it means locating prey by sensing its electromagnetic field. Every living thing generates a small electromagnetic field and this travels through water. Duck-billed platypuses are very sensitive to this and they can use it to find their prey. This is the only thing they use when they are searching for food.

Platypuses eat mostly soft food, which means they don’t need any teeth. This is lucky because they don’t have any teeth. They only have a hard lump in their mouth that they can use to grind things against. Their not having any teeth isn’t actually luck. Many millions of years ago, platypuses did have teeth, but they were out competed by another animal that ate all of their food. To survive, they evolved to eat only the soft food that the other animal didn’t eat and they lost their teeth because they didn’t need them.

So, why do they lay eggs? This is actually less odd than it sounds and is more to do with all other mammals evolving away from laying eggs. When mammals split away from reptiles, they all laid eggs. However, a couple of hundred million years ago, mammals evolved to have live births rather than lay eggs. There are several reasons for this. First is that it is safer to carry the young around with you while it is growing than it is to leave eggs in a nest. That also means that mammals need to give birth to fewer young because more of their young will survive. It also meant that the female pelvis size could be smaller because eggs have to be very large. The duck-billed platypus has gone halfway between mammals and reptiles. It still lays eggs, but it also produces milk to feed its young. Reptile and bird eggs have to have all of the nutrients in them that the growing young will need, which makes the eggs larger. The platypus gets around this by being able to produce milk that it can use to feed its young. However, they don’t have nipples, so the milk oozes out of their mammary glands and collects in folds in their skin where the babies can drink it.

Another unusual thing is that the platypus has ten sex chromosomes. For comparison, we have two. We have XX, which is female, or XY, which is male. Platypuses can have XXXXXXXXXX which is female and XXXXXXXXXY, which is male. There is no reason to have this many and researchers have no idea how it could have evolved. It could just be a mutation that didn’t have a reason. However, one of the genes in the chromosomes is the same gene that is found in the sex chromosomes of birds. This could show that platypuses are a link between mammals and birds. Because of the way they lay eggs and their reptilian gait (caused because their legs are set on the side of the bodies like crocodiles, rather than underneath their bodies like cats) they could be the link between mammals, birds, and reptiles.

They have developed webbed feet so that they can swim better, but they only have webbed front feet. When they swim, they pull their back feet in near their tails and use them to steer. They also have fur that glows a blue color under UV light. Scientists don’t know what purpose this serves, but it could be a form of camouflage for birds of prey that see UV light.

Platypuses also don’t have a stomach. Their esophagus goes straight into their intestine. This is very unusual for a mammal, but is very common for a fish or something that lives mainly on fish and things that live in water. This is very common in fish. Platypuses eat a lot of sea life, which has a calcium carbonate skeleton, which can neutralize stomach acid, making a stomach pointless.

And lastly, the males are venomous. Platypuses have a spur sticking out of each back leg that is connected to their venom gland. If they grip something with their paws, they can drive the venom spurs deep in and inject the venom. It is quite powerful and can kill many small mammals, but it doesn’t kill other platypuses or humans, although it is very painful. Researchers think that the primary use of the venom is during competition with other male platypuses. The second use would be for defense. And this is what I learned today.

Image By Charles J. Sharp – Own work, from Sharp Photography, sharpphotography.co.uk, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=143656032

Sources

https://www.sciencedaily.com/releases/2021/01/210106133034.htm

https://www.heritagedaily.com/2021/01/how-earths-oddest-mammal-got-to-be-so-bizarre/136694

https://en.wikipedia.org/wiki/Platypus

https://www.discovermagazine.com/planet-earth/why-did-our-mammal-ancestors-stop-laying-eggs

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2803040