Researchers Explain Why and How Platypus Are So Weird

Earth’s oddest mammal lays eggs, sweats milk and has 10 sex chromosomes.
Derya Ozdemir
Platypus eating wormJohnCarnemolla/iStock

There are few animals as weird as the quirky duck-billed platypus which lays eggs instead of giving birth to babies, sweats milk, has venomous spurs, 10 sex chromosomes, and a fur that glows... A newly released first complete map of its genome has added to its weirdness and provided some answers as to how a few of its unique features emerged. 

The study was published in the scientific journal Nature.

Physical map of the platypus genome

Although this beaver-like platypus native to Australia had its genome sequenced before, it was only for a female. Now, using a male platypus, an international team of researchers led by the University of Copenhagen has created a physical map of the platypus genome that is more accurate than ever before.

The duck-billed platypus belongs to a highly specialized group of mammals known as monotremes and its genes are relatively primitive and unchanged, revealing a mixture of several vertebrate animal classes: birds, reptiles, and mammals. "It has preserved many of its ancestors’ original features — which probably contribute to its success in adapting to the environment they live in," says evolutionary biologist Guojie Zhang, at the University of Copenhagen.

"The complete genome has provided us with the answers to how a few of the platypus’ bizarre features emerged. At the same time, decoding the genome for platypus is important for improving our understanding of how other mammals evolved—including us humans," Zhang said, stating that the genome holds the key as to why humans evolved to become animals that give birth instead of laying eggs.

Only animal with 10 sex chromosomes

Moreover, instead of teeth, platypus have two horn plates they use to mash their food. Roughly 120 million years ago four of the eight genes responsible for tooth development disappeared, ending up with platypus losing their teeth.

Another oddity involved how platypus is the only animal with 10 sex chromosomes. The monotremes have five Y and five X chromosomes.


Now, thanks to the near-complete chromosomal level genomes, researchers think that these 10 sex chromosomes in the ancestors of the monotremes were organized in a ring form which was later broken away into many small pieces of X and Y chromosomes.

Moreover, genome mapping has revealed that most monotreme sex chromosomes have more in common with chickens than with humans, also showing an evolutionary link between mammals and birds. Odd little animals indeed!

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