Ecdysichnia – a new ethological category for trace fossils produced by moulting

Abstract

The shedding of exoskeletons is an important aspect of the lifecycle of some in vertebrates (mainly arthropods). To rid themselves of the old cuticula (= exuvia), these animals often have to thrash about, twist around or rub themselves against the sediment or other more or less solid objects. In softgrounds, this behaviour may create distinctive patterns that have to be regarded as trace fossils. Accordingly, some ichnospecies of Rusophycus have recently been interpreted as traces made during ecdysis. Most of the so-called “Schwoimarken” from the Solnhofen lithographic limestones (Upper Jurassic, SE Germany), usually interpreted as structures made by dead organisms swaying in response to water movements, must be understood as traces of arthropod ecdysis. In this context, we erect Harpichnus bartheli igen. et isp. nov. and propose the new ethological category, ecdysichnia, for moulting traces. In most “Schwoimarken” containing body-fossil remains other than arthropods, we see sediment displacement by scavenging arthropods rather than mortichnia (sensu Seilacher, 2007). We further propose inclusion of the recently erected category pupichnia for pupation chambers as a subcategory of ecdysichnia. In our opinion, pupation is a special form of moulting that does not justify the splitting of categories, as briefly noted by Vallon et al. (2013).