Harri, Josh and Luc, Balclutha Primary School, asks :-

How did platypus come about?

Richard Laven, a veterinarian at Massey University, responded.

The platypus is one of the most unusual mammals; the group of animals which includes humans, bats, cows and kangaroos. Like all mammals the platypus has hair and feeds its young on milk. However unlike all other mammals, except for the echidna or spiny anteater, the platypus lays eggs rather than giving birth to live young.

The platypus and the four species of echidna form their own separate group of mammals called monotremes. Although there are now only 5 species of monotreme, all of which are found only in Australia or New Guinea, in the past there were many more. Fossils have also been found in South America which suggests that monotremes were originally spread across a much larger area.

The fossil evidence suggests that the ancestors of the modern-day monotremes split from the ancestors of all other mammals around 150 million years ago. It is not completely certain when the ancestors of the echidna and the platypus separated but it looks likely that they split over 100 million years ago. Fossils that are similar to the modern platypus have been found that are 25 million years old, and fossils close enough to be in the same genus have been found that are about 9 million years old, while fossils that are the same species have been found that are 100 000 years old.

Despite its appearance the platypus has no special link to birds. The so-called duck bill is nothing like that possessed by a duck; it is a highly developed organ for hunting which is sensitive to both touch and electrical currents. The platypus comes from a long-line of mammals and millions years of specialisation and isolation have resulted in the evolution of unique aquatic creature that is specialised as a hunter in Australian streams. Although the platypus is an amazing creature, its history is very similar to all other mammals having evolved over 150 million years from the same ancestor as humans.