Saturday, July 9, 2011

A Fossil Of A Different Color

Here at The Meniscus, it’s all about news in science.  Scientists are always conducting new research and new experiments, and every new experiment, if done right, leads to a new discovery, a new tidbit of knowledge to be added to the vast scientific knowledgebase, and it’s all pretty exciting.  But every now and then, science goes a step further and develops a new method of research.  A stroke of genius or an advance in technology can allow scientists to look at their subject in a way no one ever has before, and this opens the doors to a whole new realm of discoveries waiting to be made.

Every scientific discipline has its limitations.  In the field of paleontology, research is limited by the condition of fossil material.  When a prehistoric animal becomes fossilized, what typically happens is that the soft parts (hair, skin, etc.) are degraded away and the hard parts (bones, teeth, etc.) are preserved as fossils.  Now, bones and teeth are great; they allow paleontologists to interpret the diet, structure, and lifestyle of ancient animals.  But as you can imagine, not having access to the skin, blood, or internal organs of an animal really limits what you can figure out about its life.
There are, of course, exceptions.
The history of paleontology is littered with examples of new methodologies being developed and allowing researchers to look at fossils in completely new ways.  Back in the 80s, scientists began tackling the challenge of extracting genetic material from fossils, an idea that was almost unthinkable for a long time.  My undergraduate advisor once said (I’m paraphrasing here) “If you told me 30 years ago that you were gonna try to find DNA in fossil bones, I’d have said you’d had a few too many beers.”  And yet, today, scientists study ancient DNA all the time, learning more about prehistoric life than bones and teeth alone could ever have told us.  In fact, last year, an analysis of fossil DNA allowed researchers to identify an entirely new species of early man from just a tooth and a pinky bone.

It’s very important for a science to be aware of its limitations, and paleontologists are insistent upon making limitations clear.  I grew up reading books about dinosaurs, and after describing how fossils are made and how scientists research them, almost every book said the same thing: We will never know what color dinosaurs were.  They would then have a picture showing dinosaurs of all different colors to emphasize that it was impossible to know what the true color of a dinosaur was.  It wasn’t very long before I caught on that figuring out the color of a dinosaur was just never going to happen.  And if you had told the ten-year-old me that you were trying to research dinosaur colors, I would have told you – well, not that you’d had too many beers, because I was ten, but that you were crazy in any case.

And like my advisor, I would have been mistaken.

In 2008, paleontologist Jakob Vinther and colleagues took a very high-resolution look at some fossilized feathers from Brazil.  The feathers were covered in microscopic blobs that previous researchers had assumed were bacteria.  Upon closer inspection, it became clear that these blobs actually represented melanosomes – tiny organs inside cells that contain different-colored pigment molecules.  These blobs represented the structures that gave the feathers their color.

Sinosauropteryx, colorized
This was a big discovery.  Suddenly, it looked like it might be possible to guess at the color of fossil animals.  Further studies quickly showed that the researchers could do better than guess.  By examining the structure of these melanosomes, the scientists could determine what different kinds of pigments were present in the fossils, and by looking at the arrangement of these structures, it became possible for these researchers to make definitive statements about the colors of ancient organisms.  Over the last few years, numerous studies have appeared documenting the colors of ancient feathered animals, including a giant penguin from Peru, and the feathered dinosaurs Sinosauropteryx and Anchiornis, to name a few.

Exciting though these studies may be, there is a problem.  In order to analyze the microscopic pigment organelles, you need to remove a piece of the fossil to study.  Fossils are rare to begin with, and a fossil so well-preserved that you can look at microscopic cellular structures is beyond invaluable, so the fact that a specimen must be damaged slightly to determine color is less than ideal.  But once again, a new methodology has come along to save the day.  A paper published last week in Science introduces a new way to interpret color in fossil feathers. 

How does it work?  In modern animals, certain types of pigments are commonly associated with metal ions – special varieties of atoms of elements like copper, zinc, and calcium.  The pigment eumelanin, for example, which is responsible for black and brown coloration, is commonly associated with certain copper ions.  If you can find concentrations of these copper ions in a fossil, you can infer the presence of eumelanin in the fossil animal, and thus infer color!  The new study does just that – advanced scanning techniques allow Roy Wogelius and colleagues to find these copper ions in fossil remains of the two ancient birds Confuciusornis and Gansus, and from that information, they are able to determine patterns of dark coloration on the feathers of these animals.  Not only have these researchers unveiled a new technique for studying prehistoric coloration, but this new method is completely safe for the fossil – no harm done!  

Confuciusornis sanctus picture, showing dark coloration.  From the new paper, Wogelius et al. 2011.

All of the work done so far on prehistoric pigmentation has focused on fossil feathers, but pigments are found all over an animal’s body.  If these techniques can identify the color of fossil bird and dinosaur feathers, can they also be used to determine the color of the fur of ancient mammals?  How about the scales of ancient reptiles?  Skin color?  Eye color?  If these techniques take off, the future of paleontology could be very colorful indeed.

For as long as dinosaur fossils have been known to science, artists have drawn pictures of dinosaurs, swathing them in all different colors, drawing inspiration from modern day animals, drawing Triceratops gray like an elephant, or Velociraptor striped like a tiger, but now, for the first time ever, artists are choosing color patterns based on actual scientific evidence of color preserved in fossil form.

And it’s not only the artists who are benefitting from this.  Color is a major part of everyday life for all different animals.  Many animals use color as camouflage, to blend in with their surroundings; some animals, like zebras, use color to blend in with each other to confuse predators; many toxic animals are brightly colored to indicate to their enemies that they are dangerous; and many animals, from bugs to birds to baboons, use color to communicate with each other.  Knowing the color of a prehistoric animal could open the doors to all sorts of information about its lifestyle. 

I really like talking about these studies of prehistoric coloration, because it’s a great example of how the word “never” has no place in science.  There’s no reason to think, just because we can’t do something now, that we won’t be able to do it sometime later.  Who knows what other “impossibilities” we’ll shrug off years from now?  How many textbooks will say “Back in the year 2011, scientists thought this kind of study was impossible,” and what will they be talking about?  One thing is for sure:

The future is gonna be awesome.

1 comment:

  1. Nicely written, I've posted on FB so that my former geology students can have a look.