Fossil sheds light on middle ear evolution (pp 288-293)
The three tiny bones found in the mammalian middle ear are known to have evolved from components of the reptilian lower jaw. But the transition can now be seen in fossil form.

Zhe-Xi Luo and colleagues describe the fossilized remains of a primitive mammal that probably lived around 125 million years ago. The animal’s middle-ear bones remain connected to the lower jaw by Meckel’s cartilage, and the transition to the mammalian state is associated with a corresponding remodelling of the lower back region.

But the situation is not as clear-cut as it seems. The evolutionary relationships of the fossil suggest that either the modern-style middle ear evolved independently twice, or evolved and then was lost in at least one ancient lineage.

CONTACT
Zhe-Xi Luo (Carnegie Museum of Natural History, Pittsburgh, PA, USA)
Tel: +1 412 622 6578; E-mail: luoz@carnegiemnh.org

Leigh Kish (Media Contact, Carnegie Museum of Natural History, Pittsburgh, PA, USA)

Tel: +1 412 578 2571; E-mail: kishl@carnegiemuseums.org