Something that is only a blot in a slab of Silurian rock may still contain the map of an eye to where a nerve once led.
A pair of tiny, jawless fishes discovered at Lesmahagow, South of Glasgow have become a very uncharacterized lightning-rod in the engineering account of vertebrate vision. Jamoytius and Lasanius, the animals, lived some 443 million years ago, when early vertebrates are frequently viewed as anatomical guesswork since their bodies no longer possessed rigid skeletons, and their soft tissues are very uncommon to discover. However, these specimens left an adequate amount of chemical structure, which allowed scientists to recreate the appearance of the eye and tissue structures that typically fades away long before the fossilization process completes its job.
The trick was to look upon the fossils as materials rather than forms. The team scanned the fossils with an intensive beam using synchrotron X-ray fluorescence imaging that elicits telltale signals of the atoms. The signals provide element-by-element maps over a specimen, which enable investigators to relate specific chemical fingerprints to specific tissues, even where no discernible tissue still exists to the naked eye. The experiment was done in a partnership which involved imaging at the Stanford Synchrotron Radiation Lightsource where the sensitivity of the technique is capable of detecting very low elemental levels and relating them to specific microscopic anatomical structures.
The eye region in Jamoytius contained concentrated zinc and copper, which is related to the pigment and light-processing biology of the living animal, and so the retinal layer and pigment structures of a camera-like eye should be present. Small anatomical notch which was taken by the scans as the path of the optic nerve was also identified. One of the co-authors Roy Wogelius, summed up the implication of that in one technical fact: What we could find out was much more than we expected. We not only discovered some of the earliest bone structures in the depths of the geological record, but also, we also photographed the first-ever of some of the oldest camera-type eyes. Even the little notch in which the optic nerve joined has been preserved in these eyes,—the features upon which the eye of the present day vertebrates is founded today.
Another long-standing supposition, which was made difficult by this chemical method, was that early vertebrates were mainly soft in a sense that retarded the appearance of a bone-like tissue. In Jamoytius and Lasanius, scholars found patterns of elements that are associated with mineralized frameworks such as calcium and phosphorus are distributed in patterns that correspond with the location of early bone-like constituents. That is important to engineers of biological materials, since mineralization is not a single innovation; a set of controlled chemical processes or ion handling, matrix assembly, and growth control, may be present incomplete prior to the appearance of modern skeletons.
Dr. Jane Reeves has stressed the extent to which this information is not available to us with older tools: It is been astonishing to see how much new information we can get out of fossils usually too poorly preserved to be useful using these new technologies. Practically, the fossil record is considered in the study as a museum of forms and more a stable store of chemistry, of remains of biological elements, as readable after hundreds of millions of years.
The Scottish fish, put in the juxtaposition with Cambrian residues, also finds itself in a more comprehensive pattern: camera-vision visual architecture is apparent at an early stage and even richer than it had been thought. Evidence of a variety of functional eyes has been detailed, median eyes to which pigment structures and lens-like structures have been attributed, in 518-million-year-old myllokunmingids. Although they study various animals and various preservation pathways, collectively they indicate the existence of an ancient origin of the basic vertebrate camera blueprint – lens, retina, pigment control and a wiring pathway to the brain that came about earlier than several textbooks used to believe.
What is fascinating to the modern reader is not that the eyes of “ancient fish were like ours”, but that the ancient path to human sensing, deep time, could be traced in elemental residue. When high-energy imaging transforms rock into a chemical diagram, evolutionary history begins to look like a design log a log in which complex optical systems and the earliest hard tissues do emerge as initial experiments which already were technically ambitious.
