Mammalian ancestors

The earliest known mammals — dated at about 110 million years (Myr) — have been identified previously from small numbers of fossil teeth, making behavioral and anatomical comparisons difficult. In 25 April Nature, Ji Qiang and colleagues at the Chinese Academy of Geological Sciences, Beijing, report the discovery of an almost intact fossil eutherian mammal that is 125 Myr old (Nature 2002, 416:816-822).

Qiang et al. identified Eomaia scansoria (Eomaia meaning 'Dawn Mother' and scansoria denoting its probable climbing behavior) from the Yixian Formation of Liaoning Province, China, that has yielded insects and feathered dinosaurs in the past. From phylogenetic analysis they conclude that, although it is a primitive placental mammal, it probably reproduced like a marsupial. The presence of forward-extending epipubic bones and a narrow pelvic girdle suggests a short gestation period followed by parental nurture of young suspended from the abdomen.

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