Australia: The Land Where Time Began

A biography of the Australian continent 

Cambrian Explosion - Hemichordata - Ambulacraria

The earliest hemichordate, which is a crown-group pterobranch, is present in the Chengjiang Fauna together with other deuterostome phyla (Hou et al., 2011). It is believed this fossil represents a graptolite, Graptolithina, which was one of the most important of the pelagic macrofauna in the Lower Palaeozoic, continuing on into the Early Devonian. A close alliance between graptolites and pterobranchs is suggested by the tubes of the early graptolites being quite similar to those of some pterobranchs (Maletz, Steiner & Fatka, 2007), though it is not yet clear if graptolites are stem hemichordates, or possibly an extinct pterobranch branch. A possible enteroptneust hemichordate recovered from the Burgess Shale, which is still to be described, is under study at the time of writing.

Deuterostomes: Ambulacraria

Hemichordates and echinoderms are suggested by molecular data to be sister groups which form the clade Ambulacraria.

Sources & Further reading

1. Erwin, Douglas H., & Valentine, James W., 2013, The Cambrian Explosion: The Construction of Animal Biodiversity, Roberts & Co., Greenwood Village, Colorado