Platypus Genome Reveals Secrets of Mammal Evolution

Scott Norris
for National Geographic News
May 7, 2008

The genome of the platypus—our most distant mammal relative—has been decoded and analyzed, researchers reported today.

The duck-billed mammal has a genetic affinity with both reptiles and birds, according to a new study.

Decoding the platypus genome has long been an important goal for biologists seeking to understand the origins of mammal evolution.

The study, appearing in today's edition of the journal Nature, gives scientists a new window into the genetic architecture of the earliest mammals.

"The platypus genome, like the animal itself, is an amazing amalgam of reptile-like and mammal-like features," said project co-leader Jennifer Graves, of the Australian National University in Canberra.

The analysis confirms that the platypus was the earliest offshoot of the mammalian family tree, Graves noted.

The group of animals called monotremes—which includes the platypus and the closely related echidna—is thought to have split from other mammals at least 166 million years ago.

That early divergence means platypus genes carry information from a transitional point on the evolutionary time line leading from reptiles to mammals, said project leader Wesley Warren of Washington University in St. Louis, Missouri.

"The platypus is critical to helping us understand what genes were present in the ancestral reptilian lineage and how mammals evolved their particular traits," Warren said.

Eggs and Milk

Aquatic animals native to eastern Australia, platypuses have long perplexed biologists.

Although classified as mammals, they retain a number of primitive characteristics—including egg-laying—that are thought to have been passed down from mammal-like reptiles that lived over 300 million years ago.

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