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their interactive courses! [♪ INTRO] If you were to step back in time to China,
about 122 million years ago, you might have found yourself surrounded by
a flock of small creatures that looked a lot like crows, sporting glossy black
feathers with an iridescent sheen. These would not be crows, but the dinosaur
Microraptor: a little dinosaur with a bony tail, a mouth
full of teeth, and two sets of wings, with feathers on both their forelimbs and
hindlimbs. And we can describe this scene in all of this
detail because we know what this dinosaur would have looked
like, down to the colors. For a long time, we thought we’d only very
rarely know the colors of dinosaurs, or any other organism we only know from fossils. But in the past decade or so, there has been
an explosion of color. Even though fossils are basically just rocks,
with some clever paleontology and chemistry, scientists can get them to
reveal their vibrant secrets. So first off, what do we mean when we talk
about colors? On a physical level, colors in animals are
either made up of pigments, or they are what’s known as structural colors. Thirdly, there’s bioluminescence, but we’re
not going to talk about that. Pigments are molecules that absorb and reflect
specific wavelengths of light. Structural colors, on the other hand, are
a bit weirder. They don’t really have color themselves;
instead, they have microscopic structures that reflect or scatter light in specific
ways. ~ Sounds complicated, and it is complicated,
but it’s fairly common in nature. You can see it in the shiny blue sheen of
certain butterfly wings or in bird feathers. So why wouldn’t you expect to find these
colors in fossils? First off, because the outside bits of an
animal, where the color usually is, are soft and squishy and tend to not fossilize
well. And individual molecules like pigments don’t
survive the process too well either. Though the 21st century has seen rapid progress,
it’s worth noting that there have been hints that fossils could preserve at
least some form of color for a while now. We’ve known for centuries that ink from
cephalopods, the group of animals that includes squid and octopus, can actually be
preserved in fossils, for instance. Nineteenth-century fossil collectors on the
rocky Dorset coast of England would find fossil cephalopods with dark splotches in the shape of ink sacs, for instance. This fossil ink could even be re-wetted and
used to write or paint. Later analysis showed that it contained melanin,
but figuring that out required grinding up the fossils, which scientists
were reluctant to do. Scientists had also been occasionally able
to note color patterns or blotches of light and dark in things like fossil feathers, shells,
and insects before. But a major breakthrough came in 2008. And even though we’re looking for a chemical, so basically doing chemistry, the most important
tool here was microscopes. For a while, scientists had been scanning
fossils with electron microscopes, these are high-powered microscopes that can use electrons to illuminate tiny objects. Using these microscopes, they were able to
see these strange, microscopic, rod-like objects in fossils. Many people assumed that these were the remains
of bacteria, since their shape resembled that of fossil
microbes. But in that 2008 paper, researchers looking
at fossil feathers from the head of an unnamed ancient Brazilian bird advanced
a different theory: these were not bacteria, but a structure called
a melanosome. Melanosomes are cellular structures that contain
melanins, a type of pigment. The same type that is in human skin, and eyes,
and hair. In fact, melanins are a whole group of molecules, mostly black and red in color, that are made
of rings of carbon and other atoms. The scientists suggested these rod-like objects
were melanosomes because, when they compared these mysterious fossil
structures to melanosomes from the feathers of modern birds, the two
structures looked similar in terms of size, and shape, and how they
were packed together. This idea was really cool because it meant
that scientists could make guesses as to how these fossil feathers were colored,
in this case, in a stripey pattern. What’s more, the size and shape of melanosomes
in living creatures is linked to their particular color. Black and grey melanosomes tend to be long
and narrow, while red and brown ones tend to be short
and squat. So by looking at the shape of the fossil melanosomes, researchers could infer more about their color. In 2010, for instance, scientists examining
fossil melanosomes suggested that the predatory dinosaur Sinosauropteryx may
have had reddish or chestnut-colored stripes on
its tail. That same year, scientists suggested the bird-like
dinosaur Anchiornis may have had a gray body, white limbs, and
a red crest. Now, this is not a total slam dunk. People still argue about whether these are
bacteria or not. And it’s worth noting that melanosomes may
have other uses in the body besides coloration, so they might not tell
us anything about color anyway. But it’s opened up a whole field for studying
fossil color. What’s also really cool is, in living animals,
these melanosomes can combo with other structures to produce colors beyond
black and brownish-red. For instance, in the feathers of living birds,
a layer of the protein keratin over melanosomes can make them appear blue-ish
thanks to structural color. And scientists have found what they think
is evidence of this in fossils too, by comparing the exact shape of the fossil
melanosomes with extant ones used for structural color. This is why scientists have suggested that
Microraptor was that black and iridescent color. We’ve found other examples of structural
color too using electron microscopes, like in butterfly scales from the Jurassic
period. So we’ve been able to find what look like
signs of color and structures associated with color, but as scientists have
looked more at these rocks, they’ve also found specific pigments, thanks
to some heavy-duty chemistry. And the more colors we unlock, the more we may be able to infer about the
animals’ actual lives. Because it turns out we can get chemicals
from fossils. Like I said, many chemicals are too unstable
to last through time. But, it turns out, with the right conditions
many pigments are surprisingly robust. Especially in places away from oxygen, like
in lake or marine sediments, or entombed in minerals or amber. It turns out that melanins, for example, tend
to not react with water that much, which may help them stay relatively stable. Time, pressure, and temperature can still
wreck things a bit, but there’s apparently enough left that we can identify what the
original molecule was. This may involve taking a small sample from
the fossil and doing a chemical analysis, though scientists
are often hesitant to do that because fossils are so rare. But there are also more modern techniques
that mean you don’t need to touch the fossil at all. Even if the chemical structure of melanin
does break down, it leaves traces. Scientists may even be able to tell different
types of melanin, and thus different colors, apart. For example, in a 2019 paper in Nature Communications,
scientists looked at what seems to be traces of fur from a 3-million-year-old
mouse called Apodemus atavus. They used a technique called X-ray fluorescence
imaging, which involved bombarding the fossil with
X-rays, making it sort of light up based on the elements
present. Different types of melanin may contain slightly
different elements. In this case, they were looking for evidence
of zinc and sulfur, which in modern animals is associated with
the reddish pigment eumelanin. And they found them. So not only did they find a ginger mouse; they showed that we can tell melanins apart. So melanins are generally black or brown,
but we can find more colors! For instance, let’s talk about carotenoids. These are pigments, like melanin, but come
in somewhat brighter colors, like reds, yellows, and oranges. Like melanins, carotenoids can be fairly stable
in the right conditions, even over the eons. One way we’ve been able to extract them
from fossils is through high-performance liquid chromatography, or
HPLC for short. In it, a liquid solution made from the fossil
is pumped past different solid materials. And the compounds in the liquid stick to the
solid material at slightly different rates, making them move through the machine at different
speeds. This speed difference can let scientists separate and identify the individual chemicals. Another technique is Raman spectroscopy, where a sample is lit up with a laser or X-rays. The molecules in the sample scatter photons
at particular wavelengths depending on the chemicals present in it. Researchers can then filter out the wavelength
of the laser and use the remaining sample as a kind of
chemical fingerprint. Using this technique, carotenoids have been
found in the shells of ancient brachiopods, which are hard-shelled
molluscs that look kind of like sideways clams. We are still looking for examples of carotenoids
in vertebrates, though. Now those are the big players, but it’s
worth noting that there are other pigments and techniques. There’s a class of pigment called porphyrins,
for instance, that can be a range of colors including greenish
or bluish. We’ve found those in eggs and plant remains. And there are other ways to hunt for ancient
colors, like trying to detect trace elements or doing
genetic analyses of living creatures to see how ancient their
coloration genes are. And there are scientific reasons why we’d
like to know what color T. rex and friends were, in addition to just
the awesomeness factor, and having more accurate, great pictures and
drawings that we can look at. It could tell us things about how the animal
lived, like if it used its colors for camouflage
or for display. For instance, we’ve been able to find evidence
of what’s basically camouflage in an ankylosaur. A dinosaur with big, heavy protective armor,
but the researchers concluded it was under so much evolutionary pressure from predators,
it also needed to hide! Maybe we’ll even be able to identify sexual
dimorphism in dinosaurs someday, like how some modern dinosaurs have different colors between males and females. I’m talking about birds. But even though this new world of color is
exciting, there are still a few potential problems. For instance, it’s always possible we’ve
somehow gotten the chemistry wrong and what we’re detecting in any given fossil
isn’t actually pigments, but something else. And even if they are pigments, it’s possible
that they weren’t actually used for coloration. A lot of molecules play double duty in the
body. What adds color in a feather might play some
other role if it’s found in the liver or in muscle. So it’s possible we are picking up real
signals, but not thinking about them the right way. It’s also possible that, even if what we’re
seeing is coloration, we still might be wrong about the overall
appearance of the animal. Perhaps those colors were modified by some
other thing, like the keratin structures over melanin in
structural color. Or maybe they were combined with other pigments
that haven’t been preserved. Or hidden by feathers or other features. It’s also possible that this “color”
is actually contamination. Like, if the animal died and sank into an
algae-filled lake, how do we know that the pigments come from
the animal and not from the plant matter in the sediment? And, though we have made incredible discoveries
in the past ten years that have shown that finding color is possible, it’s
still the case that there may be some pigments, colors, or other structures that are just too fragile to survive in a
detectable way. We also need to be cautious about how we interpret
the color of individual fossils. You might just have gotten a uniquely colored
individual, like a black panther. And some organisms change color during their
life cycle. But we are now done with all of the hedging! That’s all the hedging we are going to do. It is amazing that now we apparently know
what color some dinosaurs were, and some other ancient animals to boot. Yes, there’s a lot of unknowns, but it is
amazing that we’re even having this discussion. A brand new field with brand new techniques has flowered in an amazingly short time. Millions and billions of years of the history
of life are a little bit lost to us. We can only observe this whole world through
the smallest of pictures, thanks to the fossil record. But now that scientists have developed amazing
techniques like these, we can start to get that picture in color. Thanks for watching this episode of SciShow,
which was supported by Brilliant. Brilliant is an online learning platform with
courses about science, engineering, computer science and math. The whole website and app are built off of
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up in a new, even more interactive format. In pre-algebra, for example, you’ll learn
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understand it on a deeper level than just learning formulas for formulas’
sake. If you’re interested, you can get started
at brilliant.org/scishow to get 20% off an annual Premium subscription. [♪ OUTRO]
