Using light to describe the ancient world

Archive for November, 2014

#Red-feathered dinosaurs?

Figure 2: Raman spectra from a fossil feather preserved in amber and from a carbonised compression fossil.

Raman spectra from a fossil feather preserved in amber and from a carbonised compression fossil.

In an earlier post I talked about the ‘insects in amber’ study that Professor Howell Edwards (University of Bradford) and his colleagues reported in 2007. In this study, Edwards et al. used a non-destructive technique (Raman spectroscopy) to analyse the bodies of insects preserved for many millions of years in amber. You can read all about it here and here.

What an amazing idea – amber is not just as a time capsule for ancient life, but also a vault for ancient biomolecules. Edwards and colleagues used this idea to learn more about insect preservation, but what else might be preserved in amber? What about feather pigments?

Birds today are highly coloured – they have colourful skin, scales, eggs, eyes, beaks… and colourful feathers. There are at least six distinct pigments that birds used to add colour to feathers. Carotenoid pigments are the most common colour molecules in the red, orange and yellow feathers of living birds. Were there carotenoids in the feathers in the ancient ancestors of birds? Did dinosaurs have red feathers?

I want an answer to this question!

My first step in getting that answer was to assemble an all-star team. Dr David Grimaldi and Mr Paul Nascimbene are amber experts at the American Museum of Natural History in New York, Dr Carla Dove (Smithsonian Institution) is a plumage expert who describes feathers at a microscopic-level, and Dr Helen James (Smithsonian Institution) is an ornithologist and paleontologist with an amazing understanding of bird evolution. Brilliant.

Next, we had a special Raman microscope shipped to us in the Birds Division at the Smithsonian Institution. This Raman microscope would let us analyse feathers in amber because it had a 1064 nm laser and confocal optics. 1064 nm is is a low energy laser, which means it doesn’t cause amber to  fluoresce (i.e. ‘glow’) – fluorescence is bad for Raman analyses. The confocal optics mean we can analyse a feather through the amber without worrying too much about the surrounding amber. Lynn Chandler at BaySpec did an amazing job of arranging the Raman microscope for us.

OK, I have the right team and the right tools, but do I have the right feathers? Carotenoids are not common in the feathers of living birds – one third of birds have feathers with carotenoid pigments, and most birds only have carotenoids on the outermost feathers. So think about it: if you randomly pluck one feather from any possible bird alive right now, the chances of that feather having carotenoids are pretty low. Imagine also that these feathers were plucked from a bird or dinosaur millions of years ago, they have to survive through deep time, be found by a paleontologist, and then be given to me for analysis. These may be be low odds, but we will never find red feathered dinosaurs if we don’t look.

Feathers in amber are amazingly precious, and we had the opportunity to work with seven ancient feathers from across the world. Alas, we didn’t find evidence for carotenoid pigments in these seven specimens. BUT, we did show that this type of work could be done without damaging the fossil feathers. It’s now just a matter of searching through every feather in amber that is found, to see if we can find our red-feathered dinosaur.

Thomas DB, Nascimbene PC, Dove CJ, Grimaldi DA, James HF. 2014. Seeking carotenoid pigments in amber-preserved fossil feathers. Scientific Reports 4, Article number: 5226 doi:10.1038/srep05226

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