By José Carlos Cortés

Etymology: Strange Wing

First Described By: Xu et al., 2015

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Saurischia, Eusaurischia, Theropoda, Neotheropoda, Averostra, Tetanurae, Orionides, Avetheropoda, Coelurosauria, Tyrannoraptora, Maniraptoromorpha, Maniraptoriformes, Maniraptora, Pennaraptora, Scansoriopterygidae

Status: Extinct

Time and Place: Between 161 and 160 million years ago, in the Oxfordian age of the Late Jurassic 

Yi is known from the Tiaojishan Formation of Liaoning, China 

Physical Description: Yi was a small proto-bird, distinctive for its truly weird appearance. Weighing about 280 grams, with a wingspan of about 60 centimeters. It had a short, blunt skull, with a very rounded front of its mouth. The front teeth were angled forward out of the mouth, giving it a slightly bucktoothed appearance. It had a fairly short and squat body. It also had a very short tail, practically not present in terms of bone structure. Its forelimbs were long and slender, with long fingers extending from the hands. Its hindlimbs are not as well known, but they were somewhat short compared to the arms. 

By Matt Martyniuk, CC BY-SA 4.0

Yi is most notable, however, for its integument. It was heavily covered in feathers, but fairly simplistic ones, long and quill like. It did not have the complex, branching filaments common to the Pennaraptoran group. These quill feathers were also fairly stiff, rather than soft and flexible. Yi was covered in a very dense coat of feathers all over its body, with the densest grouping over its body. The feet and legs were also covered in feathers. At the end of the tail there were probably long, ribbon like feathers, though those are better known from its relatives. The weirdest part of the integument, though, was the membrane extending between the fingers, covered a little by the feathers on the arms but mostly bare. This membrane was almost like that of a modern-day bat. It also connected to the styliform, a rod of cartilage grown on the wrist to help support the membrane. Yi was preserved with some color - it was mostly black all over its body, with some yellow-brown patches on the head.

By Emily Willoughby, CC BY-SA 4.0 

Diet: The diet of Yi is at least a little uncertain, though it seems likely it was an insectivore - possibly an omnivorous opportunist.

Behavior: So - could Yi fly?

Answer uncertain.

Of course I’m not going to leave it at that. But the problem is is that these wings are unique amongst dinosaurs and are, thus, hard to really compare in terms of physiology - especially since bird wings are nothing like this. Yi has been modeled in two ways - one in which the animal put together its wings like a bat (or a pterosaur) in terms of where the styliform bone was; and another in which it was more like a maniraptor; and finally a third like flying frogs. An analysis of these modes revealed that, if it was like a maniraptor, it would have had a loading capacity similar to ducks - which have larger wingspans than Yi did, indicating Yi could not fly in this model. The bat model was similar to shore birds, but this wingspan is very large and the aspect ratio is higher - again, higher than Yi. The frog model wasn’t tested. So what’s the conclusion?

Yi probably couldn’t fly.

Could it glide?

By Rebecca Groom

Maybe. 

Its center of mass was behind the control of the lift surface, which would have made it very unstable during flight. However, this was offset by a short fleshy tail and long feathers as in relatives - and it might have been able to flap a little to aid in movement, like the living Kakapo.

Either way, it’s likely that Yi spent a lot of time in the trees, climbing up and down branches and trunks in order to get food. It might have used those weird wings and tail in sexual display as well. Without more fossils, the rest is left up to speculation.

Line art by Diane Remic; coloring by Me

Ecosystem: Yi lived in the iconic Tiaojishan Formation, a late Jurassic ecosystem preserving many transitionaldinosaurs between Bird and Not-Bird, showcasing how weird and wacky almost-birds got. The Tiaojishan was a subtropical to temperate, humid coniferous forest, not unlike northern California today. It was filled with ginkgoes, conifers, cycads, horsetails, and ferns, and was extremely densely forested and lush. This, plus volcanoes nearby, lead to a very productive and diverse ecosystem. Flight was the rule of thumb for the environment, too, with so many animals in the area adapted for gliding or powered flight. Here we know not only dinosaurs, but mammals, amphibians, pterosaurs, other reptiles, fish, and invertebrates a plenty.

By Sam Stanton

When it comes to dinosaurs, almost all of them were Pennaraptorans - the kind that are especially birdie. There was Anchiornis, Auornis, Caihong, Eosinopteryx, Pedopenna, Serikornis, and Xiaotingia, a group of very early Avialans called the Anchiornithids - they were roughly at the same level of birdiness as Archaeopteryx, but looked very troodontid-y. Then there were the other Scansoriopterygids other than Yi - Epidexipteryx and Scansoriopteryx. Finally, there was the very fluffy heterodontosaurid, the maximum overpoof, Tianyulong. 

As for the cousins of the dinosaurs, the pterosaurs, there was extreme diversity as well - the weird Darwinopterans like Wukongopterus, Darwinopterus, Kunpengopterus, and Pterorhynchus; Ramphorhynchids like Fenghuangopterus, Qinglongopterux, Jianchangopterus, and Jianchangnathus; Anurognathids like Jeholopterus, and Dendrorhynchoides; an Istiodactylid Archaeoistiodactylus; and miscellaneous kinds like Daohugoupterus and Changchengopterus. All of these showcase the evolution of pterosaurs from Jurassic forms to the largers, shorter-tailed Cretaceous types! As for other reptiles, there were two unnamed lizards that had weird body proportions. 

By Ripley Cook

Amphibians are represented by many types of salamander - Pangerpeton, Liaoxitriton, Jeholotriton, Chunerpeton, and Beiyanerpeton. Mammals in this environment were fascinating too - one of the earliest tree-climbing mammaliaforms, Agilodocodon; a prehensile-tailed mammal Arboroharamiya; the semiaquatic stem-mammal Castorocauda; the burrower Docofossor; an extremely early placental relative Juramaia; the armadillo-mimic Megaconus; the rat-like Rugosodon; and the gliding Volaticotherium. There were many arthropods too, from flies to spiders to beetles to mayflies, as well as ostracods and bivalves.

Other: The phylogenetic position of Yi - and other Scansoriopterygids - is a bit of a mystery, with people arguing over whether or not they are Avialans like Archaeopteryx; basal to the group of Raptors + Avialans; or Oviraptorosaurs (Chickenparrots). Hopefully one day the mystery will be solved!

~ By Meig Dickson

Sources under the Cut 

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