The Facts About Dinosaurs & Feathers

Today, we are used to seeing feathered dinosaurs
flying around and roosting in trees. But few discoveries have so completely transformed
our picture of the extinct dinosaurs than the revelation that they had feathers, too. Or at least, some of them did. Over the past 20 years, dinosaurs of all types
and sizes have been found with some sort of fluff or even full-on plumage. But these fuzzy discoveries have raised a
whole batch of new questions. Like, exactly what kinds of dinosaurs had
feathers? And how do we know for sure? And, considering that the likes of T. rex
and Psittacosaurus couldn’t fly then what were their feathers even for? Well, find a perch and get comfortable, because
I’m here to tell you everything we know about dinosaurs and feathers. It took us a long time to make the connection
between dinosaurs and feathers — and birds in general. In fact, the first fossil to give us an inkling
that dinosaurs had feathers was actually one of the earliest specimens ever found. It was Archaeopteryx, discovered in 1861,
from the Solnhofen limestone in Germany, which dates back to the Jurassic Period. Archaeopteryx means “first wing”, and
even the 1800s, experts could immediately identify it as an ancient bird. After all, at the time, birds were the only
animals we knew that had feathers, and this thing definitely had them. But Archaeopteryx had some other features,
too — ones that were kinda strange for a bird, like a long, bony tail; fingers with
claws; and tiny teeth — things that you usually see in reptiles. Those clues suggested that birds must have
sprung from the reptilian branch of the tree of life. But no one could agree on what that actually
meant. It took decades of study and debate before
paleontologists started to see that little Archaeopteryx looked an awful lot like a dinosaur. And it wasn’t until 1996 — 135 years after
Archaeopteryx was first found — that a lucky break confirmed what they had begun to suspect. A beautifully preserved, articulated skeleton
of a chicken-sized dinosaur was found in China. And along the neck, back, and tail of this
little dino was a line of fuzz. Paleontologists named this revolutionary discovery
Sinosauropteryx It confirmed that at least some non-avian
dinosaurs had feathers, and that the history of feathers went back way farther than anyone
knew. As it turned out, Sinosauropteryx would be
just the first of many finds that would show us that dinosaurs were fluffier, fuzzier,
and more ornate than we had ever expected. The fossil record has turned out to be so
generous! In fact, the growing menagerie of feathered
dinosaurs has offered experts a pretty good outline of how feathers evolved. Dinofluff – which experts technically call
protofeathers – probably goes all the way back to the Triassic. But since dinosaurs in different times and
places had a variety of protofeather types, paleontologists are able to piece together
how feathers went from basic filament structures, to ones that allowed flight. For example, Yutyrannus,
a tyrannosaur from China, had little wisps that grew from follicles in its skin. It also represents the largest dinosaur currently known
with evidence of dinofuzz. But from those simple bits of fluff, protofeathers
became more complex over time. Dinos like the small tyrannosaur Dilong
and the tiny carnivore Juravenator had protofeathers with a central stalk that
branched off near the top. And once protofeathers started branching,
they were able to take on all kinds of new shapes. The central part of the feather became a hardened
structure called a rachis, with lots of little barbs and barbules, creating
the vanes of the feather. Dinosaurs that are closely related to birds
– like Microraptor and Archaeopteryx – had feathers like these. And interestingly, the closer you get to the
origin of birds in the dinosaur family tree, the greater the variety of feathers you find
on different parts of their bodies. So, to get a sense of how common feathers
were among the non-avian dinos, let’s take a tour of that family tree. We’ll start with this big group of two-legged
saurischian dinos: the theropods. They include everything from the crested carnivore
Dilophosaurus to the parrot-like omnivore Oviraptor. Zoom in and you’ll find a smaller group
of theropods called the coelurosaurs Every single lineage in this group has some
kind of evidence of a feathery body covering, whether it was fuzz or full-on feathers. And this is the group that includes birds,
along with a whole variety of other theropods, like the Therizinosaurs
with those enormous hand claws, and none other than T. rex. But that’s not all. All the way over on the other side of the
dinosaur family tree, there’s another, broader group called the ornithischians. They’re nowhere close to birds, in evolutionary
terms, but they have feather-like body coverings, too. Take Psittacosaurus, a
small horned dinosaur that used to run around China. It’s been found with preserved quill-like
filaments growing from its tail. Likewise, fossils of a Jurassic dinosaur from
Russia, called Kulindadromeus, show that it was nearly covered with feather-like
structures, despite the fact that it, too, was far from birds. Now, the fact that feathers and feather-like
structures show up in these very different groups of dinosaurs can mean one of two things. Either protofeathers evolved more than once
throughout dinosaurs’ history … …or they actually go all the way back to
the last common ancestor of all dinosaurs, and were retained in some groups but lost
in others. So, we have some pretty good data about the
presence of feathers within certain groups of dinosaurs. And we can use that to make informed guesses
about which particular species had feathers. For dinosaurs like Microraptor, there’s
direct evidence of feathers right there in the rock. No question about it. But then there are dinosaurs that we don’t
have direct evidence of feathers for, but we think they probably had them. This is called phylogenetic bracketing — using
the presence of traits across related species to make an educated guess where those traits
might occur. For example, most mammal fossils aren’t
found with hair, but we expect that they did have hair, because we know their relatives
do. The same goes for the likes of T. rex. Even though there’s no direct evidence of
feathers on T. rex, there’s a good chance the tyrant king was at least a little fluffy,
because other tyrannosaurs have been found with protofeathers. Ditto for Triceratops. Because its little relative Psittacosaurus
had bristles, perhaps larger horned dinosaurs did, too. And then there are dinosaurs that may or may
not have had any protofeathers at all. Will we be shocked by the discovery of an
Apatosaurus or Ankylosaurus with protofeathers someday? It’s possible. But there’s no direct evidence of that just
yet, and no one has found any fluff on any members of those dinosaur groups. So, this brings us to another question: Why? Why did dinosaurs develop feathers in the first place? Well, feathers are a great example of an exaptation. That’s a trait that evolved for one reason,
but later became modified to do something else. For instance, remember Sinosauropteryx? It lived on the ground and couldn’t fly. But its simple coat of fluff still had advantages. For one thing, feathers are great for insulation. Think of that the next time you put on a down
jacket. And they’re also really handy for display. The tail of Sinosauropteryx
was banded rust red and white, which probably helped it signal to other members of its species. And other dinosaur displays were even more
ornate! The fossilized remains of a small, strange
dinosaur called Epidexipteryx show it had long, ribbon-like tail feathers
– structures that may have been well-suited for doing the dinosaur version of a fan dance. But even as protofeathers started to get more
complex, and came to look more like the structures on the wings of birds, they still had plenty
of uses for life on the ground. For example, an amazing skeleton of the dinosaur
Citipati was found in Mongolia, with its arms in a brooding position over
a nest. Based on what we know about its relatives,
this dinosaur must have been feathered and may have used its feather-covered arms to
protect its nest. Feathered arms are also good for more active
pursuits. Studies of living birds, like chukar partridges,
have shown that birds can get a better grip on inclined surfaces, like tree trunks and
rocks, when they flap their wings as they run. Smaller feathered theropods with long feathers
on their arms, may have used this technique, possibly to evade larger non-climbing predators. And finally, feathers might have made some
dinosaurs even better hunters. Ground-dwelling dinosaurs with long arm feathers
like Deinonychus probably weren’t eviscerating their prey with those terrible foot claws. Instead, they may have acted like modern day
raptors – pinning down small prey and flapping their wings to help stabilize their grip. So, feathers had all sorts of uses. That’s what made them the ultimate dinosaur
accessory. And it’s what allowed some dinosaurs to
eventually take to the air. What evolved on the ground opened ways for
the terrible lizards to take flight, a tradition they have mostly kept to this day. But our knowledge of the when, why and how
of dinosaur feathers is still pretty new. Remember, it took nearly a century after the
discovery of Archaeopteryx for paleontologists to finally see the relationship between birds
and dinosaurs. And it took another three decades before fossils
like Sinosauropteryx started changing our view of how feathery some dinosaurs really
were. Each new find will continue to enhance our
vision of the non-avian dinosaurs. But for now, the next time that you see a
winged dinosaur flying around, feasting at your bird feeder, or standing on the head
of some statue, take a moment to appreciate the hundreds of millions of years of evolution
that made that sight possible. Thanks for joining me for this extra-feathery
episode of PBS Eons! Now, what do you want to know about the story
of life on Earth? Let us know in the comments. And don’t forget to go to and subscribe! And you’re not done exploring yet are you?! Check out some of our sister channels from
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