Article

Nature 416, 816-822 (25 April 2002) | doi:10.1038/416816a; Received 14 November 2001; Accepted 15 March 2002

The earliest known eutherian mammal

Qiang Ji1, Zhe-Xi Luo2, Chong-Xi Yuan1, John R. Wible2, Jian-Ping Zhang3 & Justin A. Georgi2

  1. Chinese Academy of Geological Sciences, Beijing 100037, China
  2. Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA
  3. Geoscience University of China, Beijing 100083, China

Correspondence to: Zhe-Xi Luo2 Correspondence and requests for materials should be addressed to Z.-X.L. (e-mail: Email: luoz@carnegiemuseums.org).

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The skeleton of a eutherian (placental) mammal has been discovered from the Lower Cretaceous Yixian Formation of northeastern China. We estimate its age to be about 125 million years (Myr), extending the date of the oldest eutherian records with skull and skeleton by about 40–50 Myr. Our analyses place the new fossil at the root of the eutherian tree and among the four other known Early Cretaceous eutherians, and suggest an earlier and greater diversification of stem eutherians that occurred well before the molecular estimate for the diversification of extant placental superorders (104–64 Myr). The new eutherian has limb and foot features that are known only from scansorial (climbing) and arboreal (tree-living) extant mammals, in contrast to the terrestrial or cursorial (running) features of other Cretaceous eutherians. This suggests that the earliest eutherian lineages developed different locomotory adaptations, facilitating their spread to diverse niches in the Cretaceous.