Scientists from the American Museum of Natural History and University of Manchester found that the ancestors of spiders had two sets of eyes, not one.
The researchers studied the X-ray images of a 305-million-year old fossil of a spider-like species called harvestman. Using the X-ray imaging enabled them to reveal the fossil's features. They also explained that successfully mapping out the features of these ancient arachnids sheds a light on their evolutionary story.
The fossil artifact of the harvestman, also called the Hastocularisargus, was located in France, and was found to have median eyes and lateral eyes. Median eyes constitute the pair of eyes at the center of the body while lateral eyes were the eyes located on both sides of its body.
To augment the results of their study, the researchers also studies the "eye stalk" gene present in harvestmen spiders living today, and they found out that, at their earliest stages, a harvestman embryo showed signs of the lateral eye.
Co-author and a postdoctoral researcher at the American Museum of Natural History, Prashant Sharma explained in a press release: "Terrestrial arthropods like harvestmen have a sparse fossil record because their exoskeletons don't preserve well. As a result, some fundamental questions in the evolutionary history of these organisms remain unsolved.
"This exceptional fossil has given us a rare and detailed look at the anatomy of harvestmen that lived hundreds of millions of years ago. What we were also able to establish is that developing modern harvestmen embryos retain vestiges of eye-growth structures seen only in the fossil."
Dr. Russell Garwood, palaeontologist in the University of Manchester's School of Earth, Atmospheric and Environmental Sciences also noted that the fossil they used for this study was very rare and that the use of X-ray imaging techniques helped them to see the harvestman's features in a more detailed manner, an event that was only a dream for scientists years ago.
Further details of the study were published in the April 10 issue of Current Biology.
