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  • This is the microraptor,

  • a carnivorous four-winged dinosaur that was almost two-feet long,

  • ate fish,

  • and lived about 120 million years ago.

  • Most of what we know about it comes from fossils that look like this.

  • So, is its coloration here just an artist's best guess?

  • The answer is no.

  • We know this shimmering black color is accurate

  • because paleontologists have analyzed clues contained within the fossil.

  • But making sense of the evidence requires careful examination of the fossil

  • and a good understanding of the physics of light and color.

  • First of all, here's what we actually see on the fossil:

  • imprints of bones and feathers that have left telltale mineral deposits.

  • And from those imprints,

  • we can determine that these microraptor feathers

  • were similar to modern dinosaur, as in bird, feathers.

  • But what gives birds their signature diverse colorations?

  • Most feathers contain just one or two dye-like pigments.

  • The cardinal's bright red comes from carotenoids,

  • the same pigments that make carrots orange,

  • while the black of its face is from melanin,

  • the pigment that colors our hair and skin.

  • But in bird feathers, melanin isn't simply a dye.

  • It forms hollow nanostructures called melanosomes

  • which can shine in all the colors of the rainbow.

  • To understand how that works,

  • it helps to remember some things about light.

  • Light is basically a tiny electromagnetic wave traveling through space.

  • The top of a wave is called its crest

  • and the distance between two crests is called the wavelength.

  • The crests in red light are about 700 billionths of a meter apart

  • and the wavelength of purple light is even shorter,

  • about 400 billionths of a meter, or 400 nanometers.

  • When light hits the thin front surface of a bird's hollow melanosome,

  • some is reflected and some passes through.

  • A portion of the transmitted light then reflects off the back surface.

  • The two reflected waves interact.

  • Usually they cancel each other out,

  • but when the wavelength of the reflected light

  • matches the distance between the two reflections,

  • they reinforce each other.

  • Green light has a wavelength of about 500 nanometers,

  • so melanosomes that are about 500 nanometers across

  • give off green light,

  • thinner melanosomes give off purple light,

  • and thicker ones give off red light.

  • Of course, it's more complex than this.

  • The melanosomes are packed together inside cells, and other factors,

  • like how the melanosomes are arranged within the feather, also matter.

  • Let's return to the microraptor fossil.

  • When scientists examined its feather imprints under a powerful microscope,

  • they found nanostructures that look like melanosomes.

  • X-ray analysis of the melanosomes further supported that theory.

  • They contained minerals that would result from the decay of melanin.

  • The scientists then chose 20 feathers from one fossil

  • and found that the melanosomes in all 20 looked alike,

  • so they became pretty sure this dinosaur was one solid color.

  • They compared these microraptor melanosomes to those of modern birds

  • and found a close similarity, though not a perfect match,

  • to the iridescent teal feathers found on duck wings.

  • And by examining the exact size and arrangement of the melanosomes,

  • scientists determined that the feathers were iridescent black.

  • Now that we can determine a fossilized feather's color,

  • paleontologists are looking for more fossils with well-preserved melanosomes.

  • They've found that a lot of dinosaurs, including velociraptor,

  • probably had feathers,

  • meaning that certain films might not be so biologically accurate.

  • Clever girls.

This is the microraptor,

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B2 US TED-Ed fossil wavelength melanin feather dinosaur

【TED-Ed】How do we know what color dinosaurs were? - Len Bloch

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    Lin posted on 2016/02/05
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