Yi is a genus of scansoriopterygid (meaning “climbing wings”) dinosaurs from the Late Jurassic of China.
Scansoriopterygids are small maniraptoran theropods, notable for their elongate third fingers and for a peculiar pelvis where the pubis is directed forwards and downwards, is proportionally short and lacks an expanded ventral end. The scansoriopterygid skull is short-faced and robust, the anterior end of the lower jaw is slightly downturned, and the teeth are procumbent.
Yi Qi (meaning “Strange Wings”) species is known from a single fossil specimen of an adult individual found in Middle or Late Jurassic of Hebei, China, approximately 160 million years ago.
It is preserved with a full coating of feathers and was a close relative of the lineage that ultimately gave rise to birds. The fossil was compressed and is visible on a stone plate and a counterplate. It is largely articulated, including the skull, lower jaws, neck and limb bones but lacking most of the backbone, pelvis and tail. Yi was a relatively small animal, estimated to weigh about 380 grams.
Like all maniraptorans, scansoriopterygids are fully feathered, but it seems that they don’t possess vaned, pennaceous feathers like those present in oviraptorosaurs, birds, dromaeosaurids and so on. Instead, they have filamentous, branching, brush-like structures of various sorts. And Yi Qi is another Mesozoic fossil dinosaur that seemingly preserves melanosomes in its integumentary structures.
Small patches of wrinkled skin were also preserved, between the fingers and the styliform bone, indicating that unlike all other known dinosaurs, the planes of Yi qi were formed by a skin membrane rather than flight feathers. On twelve positions the fossil was checked by an electron microscope for the presence of melanosomes, pigment-bearing organelles. All nine feather locations showed eumelanosomes, which cause a black colour. In the head feathers also phaeomelanosomes were present, rendering a more yellow-brownish hue. On the membranes, only one observation had a positive result, of phaeomelanosomes. The eumelanosomes of the calf feathers were exceptionally large.
Professor Xu Xing, lead author of the study from the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing said “It definitely evolved a wing that is unique in the context of the transition from dinosaurs to birds.”