A Strange Wing from the Jurassic
In 2007, a farmer named Wang Jianrong discovered a fossil in a quarry near Mutoudeng Village in China's Hebei Province. He sold it to the Shandong Tianyu Museum of Nature, where technicians began the careful work of preparing the single, remarkable specimen. What they revealed was a pigeon-sized dinosaur from the mid-to-late Jurassic Period, approximately 159 million years ago. Its scientific name, Yi qi, is the shortest of any dinosaur and means "strange wing" in Mandarin.
The strangeness comes from its wings. Unlike any other known dinosaur, Yi qi's wings were not made of feathers but of skin, similar to a bat's. This membrane was stretched between its fingers and a unique, rod-like bone extending from its wrist called a styliform element. This bone is not found in any other dinosaur but is convergent evolution, with similar structures appearing in gliding animals like bats and flying squirrels. The single known fossil, catalogued as STM 31-2, shows the partial skeleton of an adult estimated to have weighed about 380 grams (0.84 lb). The fossil also preserved impressions of wrinkled skin between the fingers and the styliform bone, confirming the membranous wing structure.
An Arboreal Glider
Yi qi belongs to an extinct family of small, tree-dwelling dinosaurs called Scansoriopterygidae, which means "climbing wings". These dinosaurs are characterized by adaptations for living in trees, including an unusually long third finger for gripping branches. The body of Yi qi was covered in simple, brush-like feathers, but these were likely for insulation or display, not for flight.
The question of how—or if—Yi qi flew is a subject of scientific study. The lack of large pectoral muscles suggests it was not capable of powered, flapping flight. Instead, paleontologists believe it was an exclusive glider, using its membranous wings to travel between trees. Studies suggest it may have been a clumsy flier compared to other small prehistoric animals, but its gliding ability was similar to that of mammals like bats. This unique form of flight was an evolutionary experiment that proved to be a dead end, leaving the feathered flight of birds as the surviving lineage. Yi qi lived in the Tiaojishan Formation, a forested Jurassic ecosystem with ginkgo trees, conifers, and ferns, and other feathered dinosaurs, early mammals, and pterosaurs.