An international team of scientists has decoded the genome of the platypus (Ornithorhynchus anatinus) and in doing so, expects to gain valuable insights into the evolution of mammals. Platypuses represent an ancient branch of mammals that today retains features of both mammals and reptiles. Now that the genome of platypuses has been sequenced, scientists can investigate the species' genetic constitution to gain a better understanding of the relationship between platypuses and their reptilian and mammalian cousins.

Like all mammals, platypuses produce milk to feed their young and their body is covered in a coat of fur. Beyond that, the similarities between platypuses and most other mammals quickly wane.

The platypus belongs to a unique group of mammals known as the monotremes. The platypus shares this group with four species of echidnas, small spiny mammals that bear superficial resemblance to hedgehogs and porcupines. Together, the platypus and echidnas represent the only group of mammals that lay eggs—a manner of reproduction associated with reptiles—instead of giving birth to live young, like all other mammals.

Until now, little information was available to discern the evolutionary history of the platypus. Few montreme fossils have been discovered and scientists could do little more than establish that the lineage was present in Australia during the Mesozoic Era, a time when Australia was still part of the super-continent Gondwana.

The platypus has a number of unique characteristics that made it an ideal candidate for genetic study. It has a bill which consists of broad horny plates attached to its upper and lower jaw. Unlike a bird's beak which is hard, the bill of a platypus is leathery and flexible except at the base where it is hard and ridged, allowing the platypus to crush and chew their food (aquatic insects, crustaceans, and plants).

Males have venomous spurs on their hind ankles that they use as weaponry against competing males when vieing for territory or mates. Their feet resemble the feet of otters. They have broad, webbed feet with strong claws enabling them to burrown into the banks of lakes and rivers.

Find out more:

• Platypus Genome Decoded (NSF)
• Platypus Genome Explains Animal's Peculiar Features (Washington University)
• Family Ornithorhynchidae (Animal Diversity Web)

Photo © Healesville Sanctuary, Victoria, Australia.