In 2007, in a quarry just outside  a village in northeastern China,   a farmer stumbled upon what seemed like  some kind of small dinosaur fossil.

A museum bought the fossil from him, and in 2015,  scientists announced that this chance discovery   was a dinosaur unlike any found before.

It was a pigeon-sized, feathered creature   from the Late Jurassic Period, around 159  million years ago.

And it seemed like a   very close relative of the earliest birds,  which also got their start around this time.

But it had one bizarre feature that had  never been seen before in any ancient   bird relative, or in any other kind  of dinosaur: bat-like membraned wings!

They named it Yi qi, which means  ‘Strange Wing’ in Mandarin.

Overnight, it showed us that there was  a lot more going on near the origin of   birds than we had previously thought.

And its differences from birds actually   makes the birds we know seem like  the weird ones in comparison.

'Cause if we take a step back, the discovery of  Yi qi forces us to ask an important question:   from an evolutionary perspective,  who really has the stranger wings?

When we think of wings, many of us   might picture feathers, probably  because birds are so familiar to us.

We're just used to feathered wings being  the default for airborne dinosaurs.

And for decades, the fossil record seemed to  back this up, with paleontologists finding   feathered dinosaurs in China and elsewhere.

And though we knew we didn't have the full   picture, the evolution of feathered wings in  theropod dinosaurs, eventually leading to flight,   was thought to have happened in a relatively  linear process of gradual refinement… …From poor flyers at first like Anchiornis,  to Archaeopteryx which could flap its wings   enough to fly in short bursts, to  the birds that fill the skies today.

And there was no evidence to suggest otherwise,  no reason to think that other bird relatives might   have taken an evolutionary detour and developed  totally different kinds of wings altogether.

But in the early 2000s, a couple  of interesting members of one   particular dinosaur family were described.

The first, in 2002, was the sparrow-sized   juvenile specimen of Scansoriopteryx,  which is also called Epidendrosaurus,   depending on which researchers you ask.

It was followed by the magpie-sized   Epidexipteryx in 2008.

And, based on some of the   unique skeletal traits of these two species,  researchers hypothesized that this family,   the scansoriopterygids, were small dinosaurs  with an arboreal, or tree-climbing, lifestyle.

These traits included their long arms,  an extended digit on each hand, and feet   that seemed adapted for perching.

So for over a decade, this family,   known only from a handful of other small fossils  from the Mid to Late Jurassic Period of China,   was just considered a strange group of dinosaurs… …One that was closely related to the lineage   that gave rise to birds and that  had adapted to life in the trees.

Now, this was already plenty fascinating  - no other non-avian dinosaurs are   thought to have been so arboreal.

But the discovery of Yi qi revealed   that there was even more to this  group than we originally thought.

The incredible level of preservation of this  specimen meant that some soft tissue elements were   still visible – including clear  evidence of a membraned wing   attached to a rod-like extended wrist  bone that gave it structural support.

It suggested that Yi qi, and probably some of  the other members of its family, were not just   climbing, but also taking to the air!

And other scansoriopterygids that were   found later provided more evidence of this.

Like Ambopteryx, which was also found by a farmer   in northeastern China and described in 2019.

It’s a close relative of Yi qi that also has   evidence of a membraned wing attached  to the same extended wrist bone.

So researchers proposed that these  dinosaurs represent a previously unknown   independent experiment in dinosaur flight.

Maybe even one of many experiments near the   origin of birds - the group that usually comes to  mind when we think of ‘winged, flying dinosaurs’.

Though, it’s hard to tell from fossils  alone whether they were capable of   powered flight – like birds and bats –  or gliding flight like flying squirrels,   though gliding seems much more likely.

One study from 2020 that modeled their   flying abilities based on their wing  structure even found that they probably   couldn’t do much more than very clumsy,  short-distance gliding between branches.

They argued that Yi qi, Ambopteryx, and the rest  of their family were not just an experiment in   dinosaur flight, but a failed experiment.

And that might be why all the species found   to date are from roughly the same time and place  in the Late Jurassic: the experiment hit a dead   end due to competition with other groups, like  the ancestors and closest relatives of birds.

It was in the Late Jurassic, after all, that  feathered wings also first appeared and gradually   became more refined for flight over time.

Eventually, this gave feather-winged   dinosaurs flying skills that were much more  impressive than anything the membrane-winged   Yi qi and its relatives had managed.

Now, while the scansoriopterygids had both   feathers and wings, they didn’t have feathered  wings, and they certainly didn't have the best   of both worlds when it came to flight.

Because their feathers, preserved   in some specimens like Yi qi, were  simple, stiff, and paintbrush-like.

They were probably used for thermal  insulation and for display, as they   were in many other non-avian dinosaurs.

In contrast, the flight feathers of birds   that cover their wings have a totally  different and more complex structure.

And because feathered wings are so successful  today, we take them for granted, and think of   membrane-winged dinosaurs as strange and unusual.

But if we take a broader view, maybe the way   we think about Yi qi and its  relatives is totally backwards.

Membraned wings aren't strange at all, really.

They’ve convergently evolved many times across   the animal kingdom, from pterosaurs  - the sister group of dinosaurs - to   mammals like bats and flying squirrels.

They show up so often for a simple reason,   too - their simplicity.

Membraned wings don't require   nearly as much evolutionary innovation.

The right mutations come together for   an area of skin to grow more than usual,  and for the arms to change to support it,   and boom, you've got yourself a membraned wing.

And these membranes often enable gliding flight,   and in some cases even powered flight, to  quickly evolve in previously flightless groups.

So, is it really surprising that  some dinos, like so many others,   went in this direction too, experimenting  with gliding flight via a membraned wing?

The fact that we saw them as strange  is more like a testament to the success   of feathered wings instead.

But birds are not normal, folks.

Flight feathers are just about the  weirdest and most complex things to   ever sprout from vertebrate skin.

And, as far as we know, in the entire   history of life on Earth, using feathered  wings as a means of flight evolved only in   birds and their closest dinosaur relatives.

And if birds were to go extinct, the skies of   planet Earth would be feather-free  and might remain that way forever.

But if every animal with a membraned wing  went extinct today, on the other hand,   you can comfortably bet that very similar  structures would show up again before too long.

They just don't require nearly  as much evolutionary innovation.

So, from a certain point of view, Yi  qi – our so-called ‘Strange Wing’ – and   the other scansoriopterygids  weren't so strange after all.

They were just one of the many diverse groups that  independently experimented with this same, simple   approach to becoming at least kinda airborne.

The unique feathered wings of birds, instead,