When: Cambrian (~500 million years ago)
What: Skara is one of the many tiny species of arthropods collected from an amazing swedish fossil locality. These fossils are notable for the intricate morphology still present, with many examples preserving individual cila, pours, and every tiny plate that makes up these animals’ shells. These fossils are made of phosphate, and what is preserved is actually a secondary coating of this compound which was deposited shortly after the animal died and was buried, thus these specimens are hollow and exceedingly fragile. Fossils with this type of preservation are called ‘orsten fossils’. This mechanism of fossilization has been found in several places around the world, the swedish locality is in Västergötland and was discovered in 1975 by Klaus J. Müller, a professor of micropaleontology at the University of Bonn. During the time of deposition, this part of Sweden, like most of the region, was covered by a shallow and warm sea.
All of these fossils are exceedingly tiny, the largest that has been found is only about 2 millimeters along its longest axis. Large animals evidently cannot be preserved by a phosphate coating. Skara is actually one of the larger specimens, coming in at a whopping 1.2 millimeters long! This form has a long flexible tail and trunk, with 5 pairs of anterior appendages. It has no eyes, and has been reconstructed as a benthic filter feeder. Skara has been placed in its own group, the Skaracarida. It is a crustacean arthropod, there are over 60,000 species of living crustaceans - including lobsters, crabs, shrimp, and barnacles, to name just a few. Within Crustacea Skara is closely related to the copepods. These tiny tiny fossils are extremely important, as they tell us a lot about the Cambrian world that was unknown to science before their discovery, such as how diverse non-trilobite arthropods already were at this early time. Additionally, as such small forms are preserved, juveniles of many fossil species are known and in some cases complete growth series.
For more information about these amazing fossils, visit the CORE website: http://www.core-orsten-research.de/index.html (Skara is in their logo!)