Evolutionary consequences of dating the Yixian Formation.

The Yixian Formation of northeastern China has yielded important new fossils that are fuelling debates on the origin of angiosperms, on the early radiation of birds and of mammals, and on the origin of feathers. Although these fossils provide a wealth of detailed anatomical information, knowledge of the absolute age of the Yixian Formation is crucial if we are to understand their true evolutionary significance. The age of the Yixian Formation has been disputed, but recent evidence provides strong support for an Early Cretaceous rather than a Late Jurassic age.