Wiwaxia - Occurrence

Occurrence

Reasonably complete specimens have been found in the Burgess Shale, middle part of the Middle Cambrian with date 505 million years ago, and fragmentary specimens in nearby strata slightly older than and younger than the Burgess Shale, in China's lowermost Middle Cambrian beds of the Kaili Formation, in the Middle Cambrian beds of the Tyrovice Member, Buchava Formation of the Czech Republic, in the Lower Cambrian Mount Cap formation (Mackenzie Mountains, Canada), in the Emu Bay Shale of Kangaroo Island, South Australia, upper Botomian Stage of the Lower Cambrian, and in the Middle Botomian Sinsk Biota of the Siberia, Russia. These finds show that Wiwaxia and most of the other Burgess Shale type fauna were very widespread. The Chinese material was originally considered to represent a separate species; like W. corrugata, it possessed spines and regions of sclerites (although it is only known from disarticulated remains), but the sclerites bear a higher density of ribs, and there are two distinct thicknesses of rib (i.e. larger and smaller). However, at a microscopic level, the sclerites do not differ from Burgess Shale or Mount Cap sclerites. The possibility remains that knob-bearing sclerites from all three localities belong to a different species. Isolates spines are more common than sclerites in localities with a poor preservation potential, suggesting that the spines were more recalcitrant; however, in well-preserved sites such as the Phyllopod bed, spine and sclerite abundance is comparable in disarticulated instances to the proportions on complete fossils.