axis of the spike. In 2010, a study was published on the soft parts visible with the "Victoria" specimen. It preserves both true impressions of the skin into the surrounding sediment, and natural casts, where the spaces left behind by the rotting of the soft body parts have been filled in with sediment. Additionally on some areas a black layer is present, possibly consisting of organic remains or bacterial mats. A part of the lower trunk flank shows rows of small hexagonal, non-overlapping, convex scales, two to seven millimetres in diameter. Higher on the flank two rosette structures are visible with larger central scales, one being twenty by ten millimetres in size, the other ten by eight millimetres. Apart from the scales, an impression of the lower side of a back plate has been found, covering about two hundred square centimetres. This shows no scales but a smooth surface with low parallel vertical ridges. As it is a true impression, with the life animal grooves would have been present. These grooves would have been about half a millimetre deep and stood about two millimetres apart. The impression probably represented the horn sheath of the plate, as would be confirmed by vertical traces of veins. It is the first direct proof of such sheaths with any stegosaurian. The study considered the presence of a sheath to be a strong indication that the plate had primarily a defensive function, as a horn layer would have strengthened the plate as a whole and provided it with sharp cutting edges. Also the display function would have been reinforced, because the sheath would have increased the visible surface and such horn structures are often brightly coloured. Thermoregulation, on the other hand — another often assumed role of the plates — would have been hampered by an extra insulating layer and the smoothness of the surface, but cannot be entirely ruled out as extant cattle and ducks use horns and beaks to dump excess heat despite the horn covering. Phylogeny In 2001 Carpenter performed a cladistic analysis showing that Hesperosaurus was rather basal and related to Dacentrurus: Carpenter was aware that his analysis was limited in scope. More extensive phylogenetic studies by Maidment recovered Hesperosaurus as a very derived stegosaurid, and the sister species of Wuerhosaurus. The position of Hesperosaurus in the stegosaurid evolutionary tree according to a study from 2009 is shown by this cladogram: