New methods promise to identify ancient proteins and pigmentation
Most of what we know about extinct animals like dinosaurs has come from their fossilized bones. Trace fossils like footprints, and even a few extraordinary cases where soft tissues have been preserved have been very illuminating, but those specimens are few and far between, only touching on a few species out of thousands that once walked the Earth. To help expand our toolkit, scientists have been looking closely at the chemistry of living and ancient birds, building new techniques to find signs of animals’ coloration and possibly even some DNA.
More persistent signs of pigment
In the past few years, scientists have been finding more and more evidence of melanin preserved in fossils. Melanin is the same pigment that colors our skin, and while skin samples do occasionally survive well enough to tell us about a dinosaur’s hide, researchers from the University of Manchester has been looking for a reliable way figure out the coloring of fossilized feathers. Rather than look for the shape of fossilized melanosomes, cell structures that make melanin, this new technique targets trace metals like zinc bonded with sulfur as an indicator of coloration. These molecular relationships have been found in the feathers of living birds, and should be durable enough to search for in fossilized specimens, even if delicate cell structures aren’t available.
Proteins saved in a shell
While there’s hope bits of zinc may hold up for millions of years, finding original proteins is a much more difficult prospect. Nobody is expecting to dig out actual DNA or other proteins from something as old as a dinosaur, because as far as we can tell, the proteins that make up DNA just aren’t durable enough to last that long. We have, however, been pushing this age boundary. It’s been calculated that after 521 years, half the bonds holding the DNA in a genome together should be degraded and broken for the average animal. Under ideally frigid conditions, more bonds might survive, which has lead to some relatively ancient genomes being sequenced, like a 110,000-year-old polar bear and a 700,000-year-old horse. Not every animal can die in the snow though, which is why researchers are still working to find proteins from other sources, like egg shells.
Eggshells were of interest thanks to their availability in a variety of climates, with ostrich shells in particular often turning up around early human archaeological sites. Previous investigations hinted that the rigid structure would better preserve fragile bits of DNA. However, as the research studied increasingly older eggshells, it turned out that relatively unstable portions of the shells’ molecular structure were the real safe-havens for DNA. The oldest shell used in the study was 3.8 years old, and while only a portion of a protein survived, the fact that it could be found at all was remarkable. This doesn’t mean that we’ll have an ancient ostrich’s genome sequenced in the near future, but it can act as a template for other studies. As these techniques become more and more refined, we may discover more protein data among our fossils than anyone would have hoped.
Source: Ancient eggshell protein breaks through DNA time barrier, Scienmag