Editor's Summary

15 March 2007

An early look at mammals

The formation of the three tiny bones of the middle ear from components of the reptilian lower jaw was a key event in mammalian evolution. Never before has this transition been seen so clearly as in a primitive fossil mammal found recently in a new locality of the Yixian Formation in China, 300 km west of the classic sites in Liaoning. In this specimen the middle-ear bones remain connected to the lower jaw by Meckel's cartilage — a transition associated with a corresponding remodelling of the lower back. But the situation is not as clear-cut as it seems. The evolutionary relationships of the fossil suggest that either the 'modern' middle ear evolved twice, independently or that it evolved and was then lost in at least one ancient lineage.

ArticleA new eutriconodont mammal and evolutionary development in early mammals

Zhe-Xi Luo, Peiji Chen, Gang Li & Meng Chen