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Jurassic Ink

May 29, 2012

As a necessity, scientists of my generation often became expert draftsmen. Draftsmen are also known as draughtsmen, although beer is usually not involved. There were no computer applications for creating publication-quality data plots or diagrams, so everything was drawn by hand. In my case, the drawing often involved schematics of electronic circuits, which are somewhat more complicated than most drawings.

To do this drafting, I had a set of metal compasses, rulers, triangles, and circle templates; and I also had an exquisite set of pens (see photo). These pens were engineered to produce lines of precise width using India ink , a colloid of fine carbon soot in an aqueous vehicle. Lines made with India ink are very opaque, and they are easily reproduced.
Staedtler pen setStaedtler Mars pen set,
circa 1980.

Photograph by author.
Since India ink is made from carbon particles, these form a percolation network of low conductivity when the ink dries. Thus, India ink allows attachment of wires to measurement specimens when a highly conductive attachment is not required. It is especially useful in high voltage circuitry to allow a very high resistance ground return for components.

Octopus ink has had been used as a plot thickener in cartoons, but in antiquity it was actually used as an ink. The color, sepia (color code #5E2612), is associated with the ink of one order of cephalopods, the cuttlefish, which was harvested for ink.

Figure captionDrawing of a cuttlefish (Sepia officinalis), from the 1911 edition of Webster's Dictionary.

(Via Wikimedia Commons).

Ink is nearly ubiquitous among cephalopods, so a natural question would be when such an evolutionary adaptation got started, and whether ancient cephalopod ink was different from modern ink. The problem here is that you need a specimen of primordial ink. A large international team of scientists has analyzed traces of ink from two ink sacks associated with fossils of 160-million-year-old giant cephalopods from the Jurassic period.[1-2] The fossils were discovered two years ago in England.[1]

They found chemical traces of melanin, a common biological pigment for both plants and animals. The chemical structure was essentially identical to the melanin (specifically, eumelanin) found in the ink of modern cuttlefish.

Structural unit of eumelaninEumelanin, a common biological pigment.

(Structural diagram by Roland Mattern, modified, via Wikimedia Commons).

The fossils with ink sacks were found in Christian Malford, Wiltshire, England, somewhat west of London, by Phillip Wilby of the British Geological Survey. One of the ink sacs is the only intact ink sac ever discovered.[1]

Wilby sent samples to John Simon, a chemistry professor at the University of Virginia, and Japanese chemist Shoskue Ito, both of whom are experts in melanin. Simon and Ito assembled an international team with members from the United States, the United Kingdom, Japan and India, to chemically examine the fossil evidence in search of melanin, which was found.[1]

Figure captionAn ink sac from a Jurassic age giant cephalopod fossil, found to contain the pigment, melanin.

(University of Virginia image, used with permission).

That melanin, an organic compound, should survive after 160 million years, seems quite remarkable, since animal tissue decomposes quickly. Melanin, however, is more resistant to decomposition, since it's polymeric. Says Simon,
"Out of all of the organic pigments in living systems, melanin has the highest odds of being found in the fossil record... Though the other organic components of the cephalopod we studied are long gone, we've discovered through a variety of research methods that the melanin has remained in a condition that could be studied in exquisite detail."[1]
The chemical composition of the trace evidence of melanin matched the melanin of modern cuttlefish ink. This affirms the possibility that the ink cloud defense mechanism of such creatures hasn't changed since the Jurassic. Says Simon, "The whole machinery apparently has been locked in time and passed down through succeeding generations of cuttlefish. It's a very optimized system for this animal and has been optimized for a long time."[1]

A paper on this research has been published in the May 21, 2012, issue of the Proceedings of the National Academy of Sciences.[2]

References:

  1. Fariss Samarrai, "Cephalopod Ink from Jurassic Period Identical to Modern Cuttlefish Ink, U.Va. Study Shows," University of Virginia Press Release, May 21, 2012.
  2. Keely Glass, Shosuke Ito, Philip R. Wilby, Takayuki Sota, Atsushi Nakamura, C. Russell Bowers, Jakob Vinther, Suryendu Dutta, Roger Summons, Derek E. G. Briggs, Kazumasa Wakamatsu and John D. Simon, "Direct chemical evidence for eumelanin pigment from the Jurassic period," Proc. Natl. Acad. Sci., online before print May 21, 2012, doi: 10.1073/pnas.1118448109.