Why platypuses are mammals

He and his colleagues study a family of genes called relaxins that are involved in a variety of mammal-specific biological processes including nipple development and cervical softening, as well as testicular descent.

When the platypus genome became available for study, Hsu was eager to compare the sequence of their relaxin genes with that of relaxin family members from fish, birds, marsupials and placental mammals.

INSL3 interacts with a receptor called LGR8 and has been shown to be critical to testicular descent, while RLN3 interacts with a related receptor called LGR7, which has been implicated in mammary gland and nipple development. The ancestor gene, however, showed no such bias.

In fact, it was equally able to activate either receptor. The real tipping point, Hsu discovered, occurred when the ancestor gene was duplicated in a way that was likely a genetic fluke.

This type of random event is thought to be important in evolutionary leaps, such as the development of a placenta, that are difficult to explain by the ongoing gradual accumulation and selection for minute changes, such as beak shape or coat color. In the case of the INSL3 ancestor, the duplication fluke occurred sometime before the monotremes, marsupials and placental mammals split, but after fish and frogs became separate groups.

The presence of two identical copies of the ancestor gene freed one copy from the selective pressure that had likely restrained its evolution and allowed it to mutate and attain new functions while losing others.

Hsu found that fish, which became a separate group before the duplication, maintained ancestorlike genes that activate both receptors. Current Population Trend: Decreasing. Share Tweet Email. Go Further. Animals Wild Cities This wild African cat has adapted to life in a big city. Animals This frog mysteriously re-evolved a full set of teeth. Animals Wild Cities Wild parakeets have taken a liking to London. Animals Wild Cities Morocco has 3 million stray dogs. Meet the people trying to help.

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Both the platypus and the echnida are monotremes, meaning that they lay eggs and have a single opening cloaca for reproduction and elimination of wastes. Home Ocean Facts What is a platypus? What is a platypus? Skip to content. Read later. You don't have any saved articles. By Emily Osterloff. Unusual features Despite its odd look, the platypus is perfectly adapted to its environment. How the platypus got its name George Shaw, keeper of the natural history collections at the British Museum which were to later become the Natural History Museum , accepted the platypus as a real animal.

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