Yi

Yi qi represents one of the most bizarre and unexpected discoveries in dinosaur paleontology. This tiny theropod, whose name means "strange wing" in Mandarin Chinese, possessed a flight apparatus unlike any other known dinosaur. While birds evolved feathered wings and pterosaurs had membrane wings supported by an elongated fourth finger, Yi qi took an entirely different evolutionary path — developing bat-like membranous wings supported by an elongated third finger and a completely unique rod-like bone extending from its wrist called a styliform element.

Discovered in 2015 by a farmer in Hebei Province, China, the single known specimen preserves remarkable soft tissue impressions including patches of membrane between its fingers and along its arms. The fossil dates to approximately 159 million years ago during the Late Jurassic period, when this region was a lush forest ecosystem. Yi qi likely inhabited the trees, using its unusual wings to glide between branches in search of insects and other small prey.

Despite having both feathers and membranous wings, Yi qi was probably not a powerful flier. Biomechanical studies suggest it was more likely a glider, similar to modern flying squirrels, rather than capable of sustained powered flight like birds. Its small size — roughly comparable to a pigeon — and lightweight skeleton were adaptations for this arboreal, gliding lifestyle.

The discovery of Yi qi fundamentally changed our understanding of dinosaur flight experimentation. It shows that multiple lineages of small theropods independently evolved different solutions to becoming airborne during the Jurassic period, with birds ultimately becoming the most successful. Yi qi's lineage, the scansoriopterygids, represents an evolutionary dead end — a fascinating "what if" in the history of flight.