best explanation is that the trackways were formed on bedforms produced on a river bed, but while they were exposed by a low-flow period. Beaconites antarcticus: narrow, parallel grooves, about an inch apart, disappearing into elliptical pits; created by shovelling the surface sediment aside before burrowing into the sediment. Occasionally branch. Perhaps B. barretti: more widely spaced grooves (~3 cm); small footprints visible. Implies many walking limbs and an approximately rectangular shape — reminiscent of trilobites. Extend laterally up to ; burrow deeply into sediment. Probably produced by a very different arthropod to B. antarcticus. Large (~30 cm wide) trails with a scrape mark from a central tail. Three to four footprint pits diverge from these tracks at a high angle. The feet making the footprints had spines on their rears. These may have been formed by eurypterids but are not a perfect match to known eurypterid trails; they may also have been formed by xiphosurans Diplichnites trackways: double rows of fossils previously attributed to marine trilobites but now thought to perhaps be formed by annelids or myriapods. Here they appear on metre-scale crossbeds that may represent sub-fluvial dunes. Cruziana and Rusophycus: thought to be formed by trilobites, whose body fossils are found only in marine assemblages. Could also have been made by other arthropods, or the lower parts of the Beacon Sandstone may have been marine. They have been found in many other non-marine instances. Skolithos: traditionally thought to be marine; however, there are many counterexamples. References Further reading Geography of Antarctica Geology of Antarctica Geologic formations of Antarctica Geological supergroups Fossil trackways Trace fossils