Imaging techniques in the study of fossil spiders

Spiders are the most diverse and important terrestrial predators in modern ecosystems. Therefore, fossil spiders are fundamental to understanding past terrestrial ecosystems, especially coevolution with their principal prey, the insects. Being generally soft bodied, spiders have a poor fossil record, but where they do occur, it is in the exceptional circumstance of a Fossil-Lagerstätte. By far the greatest number of fossil spider specimens are found in amber (fossilized tree resin), but earlier than the Cretaceous and outside of amber forest areas, rock-matrix preservation is essential for the spider fossil record. Every taphonomic situation requires a special technique for study. Here, we review imaging techniques in the study of fossil spiders. The earliest depictions of fossil spiders are drawings made with the unaided eye. Light microscopy enabled detailed drawings to be produced and, later, photographs of fossil spiders appeared in the literature. In the 21st century, digital photography has revolutionized image capture and reproduction, and scanning electron microscopy has been applied recently to fossil spiders. The most exciting modern technique, X-ray (including synchrotron source) CT scanning, is now producing extraordinary images of three-dimensional fossil spiders embedded in amber, and the method is also applicable to rock-matrix preservation. We expect to see considerable refinement of these techniques in the future, as well as the possibility of novel ones. Thanks to the excellent preservation of some fossil spiders, and modern techniques available to provide exquisite images of fine morphological details, fossil spiders can now be considered taxonomically (sub)equal to modern forms. Hence, the usual excuse for excluding fossil spiders in phylogenetic and other studies no longer carries as much weight as it once did, and we encourage neontologists to consider the fossil record whenever possible.