Conifer cones bear their ages well, and still move it

Cones from coniferous trees like pines open in response to dry conditions and close in response to wet conditions -- a mechanism that enables them to release their seeds under favorable environmental conditions. In addition, the movement of the individual scales is passive, meaning that it does not require any metabolic energy. These attributes have recently brought conifer cones to the attention of scientists, who aim to use them as biological models for the development of technical devices capable of autonomous movement. Poppinga and Speck have now discovered that the scales continue to function in this way for an extremely long time: Fossil cones from the Eemian interglacial period, about 126,000 to 113,000 years ago, as well as the middle Miocene, about 16.5 to 11.5 million years ago, still react to changes in moisture by moving their scales. With the help of x-ray-computed tomography, the researchers demonstrated that the cones are preserved by coalification during the fossilization process and that the fossilized cones show only very few mineral inclusions. This ensures that the fine structures responsible for moisture-dependent movement remain intact.