An article published in the journal “Current Biology” describes the discovery of two species of dinosaurs belonging to the Alvarezsauria group, which shares many characteristics with modern birds, in north-western China. A team of researchers studied the fossils of the species that were named Xiyunykus pengi and Bannykus wulatensis recognizing some characteristics intermediate between the oldest species of that group and others that lived several million years later, showing for example how the morphology of their arms evolved slowly.