Halkieriid

The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is Halkieria .

The group is sometimes equated to Sachitida, although as originally envisaged, this group includes the wiwaxiids and is thus equivalent to the Halwaxiida.

Occurrence

The only reasonably complete specimens, of Halkieria evangelista, were found in the Sirius Passet lagerstätte in Greenland. Fragments which are confidently classified as belonging to halkieriids have been found in China's Xinjiang province and Australia's Georgina Basin, while shells of a possible halkieriid have been found in Canada's Burgess Shale. Halkieriid-like armor plates, called "sclerites" have been found in many other places as part of the small shelly fauna.

The earliest known occurrences of Halkieriids sclerites, classified as Halkieria longa, date from the Purella antiqua Zone of the Upper Nemakit-Daldynian Stage in Siberia. The mass extinction at the end of the Cambrian period's Botomian age was thought to have wiped out most of the small shellies, including the halkieriids, but in 2004 Halkieriid fossils classified as Australohalkieria were reported from Mid-Cambrian rocks of the Georgina Basin in Australia. It is not known why this clade would have survived while other halkieriid clades apparently died. It may be significant that the only archaeocyathans known to have survived the end-Botomian extinction also occur in Gondwana, the old super-continent that embraced South America, Africa, India, Australia and Antarctica.