Yi: Beast of the Week

 This week we will be checking out a dinosaur that was so unusual, it completely changed what we thought we knew about dinosaur evolution.  Check out Yi qi! (pronounced "EE-chee")

Yi was a small theropod dinosaur that lived in what is now Hebei, in Northeastern China during the late Jurassic period, about 159 million years ago.  From snout to tail it only measured about a foot (30 cm) long and its wingspan was about 2 feet (60cm) wide.  The genus came, "Yi" translates from Mandarin to "wing" and the species name, "qi", means "strange", which is totally appropriate as you are about to find out.  It also fun to note that Yi qi has the shortest full name of any dinosaur.

Watercolor reconstruction of Yi by Christopher DiPiazza.

Yi belonged to the family of theropod dinosaurs, called scansoriopterygidae, which are known for being relatively small, with short snouts and teeth in the front of their jaws that jutted forward, possibly an adaptation for grabbing insects.  They are also known for having feathers and extremely long fingers, often portrayed living in trees.  These traits alone make them stand out among dinosaurs, but what makes Yi even more unusual is the fact that it had a sheet of skin stretching from its fingers and down its arms, which was supported by an extra rodlike bone that grew out of its wrist, forming what can only be described as batlike wings.  Before this we only knew of animals evolving wings three times in vertebrates, bats, pterosaurs, and dinosaurs(feathered wings seen in birds).  Now it turns out that dinosaurs evolved a second completely different version of wings alongside the feathered ones thanks to Yi.  It should also be noted that modern gliding mammals, like flying squirrels possess an elongated piece of cartilage near their wrist, extremely similar to the bone growing out of Yi's.  All of these features suggests Yi was likely at least gliding around when it was alive.  The experts who originally described Yi suggested it may have even been capable of powered flight but more evidence is needed to prove it.  

Diagram showing the homologous parts of the wings of each kind of vertebrate.  Thanks to Yi we know dinosaurs evolved wings at least two separate times.

What makes Yi even more interesting is despite having batlike wings, its body was mostly covered in feathers. The feathers themselves were preserved enough to tell they each comprised of a quill with a little tuft at the top, essentially mini palm tree shaped.  They start almost at the tip of the dinosaur's nose and go down the head and neck, cover the torso extending to the arms, and also on the legs down the shins.  Scientists were also able to find melanosomes (organelles that determine pigment in hair, skin, and feathers) preserved in both the feathers and skin of Yi.  According to the melanosome shapes that preserved, Yi may have had reddish colored feathers on its head, gray or black feathers on its body, and dark gray or black colored skin on its wings. (Keep in mind this is only based on the melanosomes they were able to find.  Sometimes animals have a variety of different melanosomes that when together reflect different colors, some that maybe don't preserve well.)

The unusual appearance of Yi doesn't even there. A close relative of Yi's, called Epidexipteryx, was discovered with four long ribbon-like feathers growing out of its otherwise stumpy tail. Sadly Yi's tail wasn't found, but it is possible it also sported feathers like this.  We can't be sure what they would have been for, likely display of some kind if it was anything like its modern bird relatives. 

Photograph of the found fossils of Yi qi from the paper by Xu et al. referenced below.

All of these unusual traits lead most experts to think Yi was a tree dweller in life.  It could have used its strong arms and long fingers to climb, and probably was able to glide at least short distances between branches.  Its short face and small teeth would have been a good for eating insects, but it may have been omnivorous too, nibbling seeds or other plant matter.  The fossils of many other interesting creatures have been unearthed in the same area as Yi, including fellow dinosaurs, Anchiornis, Eosinopteryx, and Tianyulong, the pterosaur, Darwinopterus, as well as the salamander Chunerpeton, to name a handful. 

References

Dececchi, T. Alexander; Roy, Arindam; Pittman, Michael; Kaye, Thomas G.; Xu, Xing; Habib, Michael B.; Larsson, Hans C. E.; Wang, Xiaoli & Zheng, Xiaoting (2020). "Aerodynamics Show Membrane-Winged Theropods Were a Poor Gliding Dead-end". iScience. 23 (101574) 101574.

Xu, Xing; Zheng, Xiaoting; Sullivan, Corwin; Wang, Xiaoli; Xing, Lida; Wang, Yan; Zhang, Xiaomei; O'Connor, Jingmai K.; Zhang, Fucheng & Pan, Yanhong (7 May 2015). "A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings". Nature. 521 (7550): 70–73.