Calimari Calligraphy: Same Ink, 160 Million Years Later

Old news: Geologists, digging up ancient British sea bed, unearth a fossilized cephalopod.


Big news: Its pigment sacs contain the same ink squid still use today!

Fossilized Ink Sac
Source: British Geological Soc. | Nat Geo

This archaeology, with a dash of chemistry for good measure, went to press in PNAS earlier today. As Nat Geo, Discovery News, and msnbc tell it, a stroke of luck brought the multi-national (Japan, India, USA, UK) team a fully intact ink sac, which still contained eumelanin, the ubiquitous black pigment found in skin, hair, and feathers throughout the biological world (for more on the structure and function of melanins, click here).  


Quoth the lead author, John D. Simon (UVA-Charlottesville), to Discovery: 

"Out of all of the organic pigments in living systems, melanin has the highest odds of being found in the fossil record" 

In other words, this collection of highly-oxidized tyrosine and indoleacetic acid residues, chained into polymeric pigments, stays preserved - and structurally sound - for 160 Million Years. Could we say that about most of the materials we make today? Moreover, by comparison of various spectral techniques, the authors wager that the ancient melanin composition looks nearly identical to what squid use today to scare off predators.

IR Data, "flipped"
Source: PNAS Supp Info

Well, I'd like to see some data, wouldn't you? Digging through the Supporting Info, I see loads of evidence: degradation studies, EPR, IR, Mass Spec, CHN analysis, Carbon-13 NMR, UV, pyrrolysis TIC, and X-Ray photoelectron spectroscopy (Whew!). 


Let's examine two of these a little closer. For the IR data, I've switched the view around 180 degrees, to present the peaks the way you'd normally see 'em in the lab. Note the top 2, calcium carbonate and hydroxyapatite, with their nice, sharp C=O and P=O stretching bands. When the researchers looked in the partially-fossilized sediment, they found mostly these two...but look at the dye! Even after all those millennia, the absorbances for the fossil dye line up almost perfectly with the modern-day sample.

Total Ion Chromatogram, Current (top) vs. Fossil (bottom)
Source: PNAS Supp Info

How about a little heat? If you cook the ink at 600 Celsius, then pass it quickly through a mass spec, plotting ion current vs. time, you get the next spectrum, the TIC. It shows the same breakdown products, a variety of small heterocycles and fatty acids, and something I wasn't familiar with: diagenetic products. These products, formed from reactions that occur during fossilization, show up here as sulfur heteorcycles. Since the samples have had quite a bit of time underground, they show much more diagenetic decomposition.