Jurassic Squid Ink Very Similar To Modern Squid Ink
An international team of scientists have for the first time discovered two 160-million-year-old giant cephalopod fossils with intact ink sacs that contain dried pigment similar to that of modern cuttlefish.
The researchers, of which includes a professor from the University of Virginia, said the ancient brownish-black pigment, known as eumelanin, is widespread in the animal kingdom in squid ink, bird feathers and even human hair and skin. And because the fossilized pigment is so similar to that found in squid ink today, the researchers suggest this defensive weapon has not evolved much since the Jurassic era.
Scientists have found traces of eumelanin in other fossils in previous studies, but through indirect and less reliable means, according to study co-author John Simon.
In this study, published online in the journal Proceedings of the National Academy of Sciences, Simon and colleagues used a variety of high-resolution chemical techniques — including scanning electron microscopy and mass spectrometry — to identify eumelanin in the fossilized ink sacs.
Amazingly, the fossilized ink sacs escaped decomposition, providing scientists with “exceptional” soft tissue specimens for studying, said the researchers. One of the ink sacs studied is the only intact ink sac ever discovered.
“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,” said Simon, a chemistry professor and the executive vice president and provost at U. Va. “We all got pretty excited about looking at these ancient fossils.”
The fossils were found by Phillip Wilby of the British Geological Survey in an ancient seabed at Christian Malford, Wiltshire, England. He sent the samples to Simon and Japanese chemist Shoskue Ito, both experts of melanin. Simon and Shoskue reached out to other experts in the field from the UK, the US, Japan, and India and started investigating the samples to see if the melanin had in fact been preserved.
Once they determined the melanin was preserved, they compared the composition to the modern Sepia officinalis, and found a surprising match.
“It´s close enough that I would argue that the pigmentation in this class of animals has not evolved in 160 million years,” said 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.”
Animal tissue usually degrades very rapidly. Over millions of years typically all that is left is skeletal remains or an impression of the shape of the animal in surrounding rock. Scientists can learn a lot by these fossilized remains, however, without organic matter there are many questions that cannot be answered. But melanin has proven to be an exception. Although it is organic, it is highly resilient to degradation, said the researchers.
“Out of all of the organic pigments in living systems, melanin has the highest odds of being found in the fossil record,” said Simon. “That attribute also makes it a challenge to study. We had to use innovative methods from chemistry, biology and physics to isolate the melanin from the inorganic material.”
“As we look back and think about what we know about life before our time, it’s mostly through skeletal info,” he told National Geographic. “What´s beginning to happen now is that people are realizing that, in addition, there is soft tissue that´s being preserved.” Studying soft tissue “could give us a whole new window into species that are extinct and their relationships to modern-day” life-forms, he added.
To be sure of their findings, the team cross-checked their work using separate experiments designed to exploit the various molecular features unique to melanin and determined the morphology and chemical makeup of the material — a combination of in-depth, multidisciplinary techniques that are not normally used by paleontologists to study fossil samples.
“I think the strength of this paper is that it is not tied to a single method,” Simon said. “Any one technique would have brought some insights, but potentially more questions than insights. It was really the more holistic approach that fully characterized it and allowed us to actually do a real comparison between what existed during the Jurassic period and what exists now.”
Image 2 (below): An ink sac from a 160-million-year-old giant cephalopod fossil contains the pigment melanin; it is essentially identical to the melanin found in the ink sac of a modern-day cuttlefish. Credit: University of Virginia