The duck-billed platypus (Ornithorhynchus anatinus) is a small mammal. It is one of only two monotremes to survive today. It lives in eastern Australia. The plural of platypus is just 'platypus'.
The platypus lives in rivers and river banks. It is one of only two families of mammals which lay eggs. The other is the Echidna, which has four species. The platypus was first described in detail in the early 19th century, but it took a while before biologists in England believed what they were reading.
These mammals are called monotremes because they have a common rear opening known as the cloaca. Through this opening faeces and urine are voided (put out), and sexual activity takes place. This is a primitive ('basal') feature of tetrapods, which monotremes, birds and reptiles have today. The more 'advanced' ('derived') mammals have the system where the rear has two openings.
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