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Mother of All Marsupials

12 December 2003 (All day)
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Fur and all. This 15-centimeter-long early marsupial skeleton is astonishingly well preserved.

Last year, the fossil beds of Liaoning Province, China, yielded the most primitive placental mammal ever found. Now comes another record-breaker: the most ancestral marsupial known, in such good shape that even some of the fur is preserved. Described in today's issue of Science, the mouse-sized fossil will provide a wealth of information on how the earliest marsupials evolved.

The team--led by Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh and Qiang Ji of Nanjing University, China--identified the fossil as a marsupial relative through features of its wrist, ankle, and teeth. At 125 million years, the new fossil--dubbed Sinodelphys szalayi--pushes back the record of marsupials by 15 million years. (Molecular data suggest that the group could be as old as 190 million years.)

It's extremely rare to find an entire mammal skeleton this old, so it should provide a "rich source" of clues to the evolution of the marsupials, note Richard Cifelli and Brian Davis of the University of Oklahoma, Norman, in an accompanying commentary.

For example, the shoulders, limbs, and feet of Sinodelphys imply that it could climb trees and bushes. That's true of Eomaia, the early placental from Liaoning, but not of more primitive mammals of the same period. To Luo and his co-authors, that implies that climbing skills were important adaptations that helped evolve into new species.

Related sites
Eomaia, the early placental mammal (ScienceNOW, 25 April 2002)
More about marsupials

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