Diagonella Cambrian Explosion Fossil Sponges Assemblage

Description: Diagonella belongs to the family Protospongiidae, which was a group of early and primitive sponges of the Class Hexactinellida. Diagonella was attached to the sea floor by long spines at the base of the sponge. These spines are rarely preserved. The six-rayed spicules were not fused into a net, so were relatively fragile as a result. These sponges are very rare in the Burgess Shale of British Columbia, and sponges are relatively uncommon in the fossil record owing to their delicacy. This specimen exhibits unusually fine preservation.

Sponge fossils from the Cambrian Explosion are found in various Cambrian sites in North America, most notably the Burgess Shale of Canada, and the Cambrian strata of Utah, unlike this specimen, which comes from a new location. Many sponges are also described from the Chengjiang biota of China. Sponges are believed to have undergone repeated radiations in the Phanerozoic, and probably attained their largest diversity in the Cretaceous.

This assemblage of five examples comes from the Comet Shale Member of the Pioche Formation of Nevada. This deposit spans the transition of Early to Middle Cambrian which saw the extinction of the Olenellid trilobites. It is just younger than the comparable material from the Chengjiana Biota of Yunnan Province, China and just older than the Burgess Shale Fauna of British Columbia, Canada. The specimens are often somewhat faint, as here. The specimen has been water wet to heighten contrast in the last photographs. Regardless, this is a rare specimen, little seen outside of an academic collection. Most of the outcrops are on BLM land which is not available for collecting. This material however comes from a ranch on private land.

Reference: A New Soft-bodied Fauna: The Pioche Formation of Nevada, Bruce S. Lieberman, Journal of Paleontology, Jul 2003.