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Science 12 December 2003:
Vol. 302. no. 5652, pp. 1934 - 1940
DOI: 10.1126/science.1090718
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Research Articles

An Early Cretaceous Tribosphenic Mammal and Metatherian Evolution

Zhe-Xi Luo,1,2* Qiang Ji,2,3 John R. Wible,1 Chong-Xi Yuan4

Derived features of a new boreosphenidan mammal from the Lower Cretaceous Yixian Formation of China suggest that it has a closer relationship to metatherians (including extant marsupials) than to eutherians (including extant placentals). This fossil dates to 125 million years ago and extends the record of marsupial relatives with skeletal remains by 50 million years. It also has many foot structures known only from climbing and tree-living extant mammals, suggesting that early crown therians exploited diverse niches. New data from this fossil support the view that Asia was likely the center for the diversification of the earliest metatherians and eutherians during the Early Cretaceous.

1 Carnegie Museum of Natural History, Pittsburgh, PA 15213, USA.
2 Department of Earth Science, Nanjing University, Nanjing 200017, China.
3 Chinese Academy of Geological Sciences, Beijing 100037, China.
4 China University of Geosciences, Beijing 100083, China.

* To whom correspondence should be addressed. E-mail: luoz{at}carnegiemuseums.org

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Science. ISSN 0036-8075 (print), 1095-9203 (online)