Sphenothallus is a problematic extinct genus lately attributed to the conulariids. It was widespread in shallow marine environments during the Paleozoic

Paleozoic

The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

.

Occurrence

Sphenothallus is represented in the Cambrian period in the Kaili biota and the Mount Stephen trilobite beds

Mount Stephen trilobite beds

The Mount Stephen trilobite beds are a series of fossil strata on Mount Stephen, British Columbia that contain exceptionally preserved fossil material...

, where it co-occurs with the similar organisms Cambrorhythium and Byronia

Byronia

Byronia is a genus of theca-bearing cnidarian with a close affinity to the coronatidscyphozoans....

. It is known in younger strata in Canada and the USA, surviving at least until the Mississippian.

Ecology

Sphenothallus lived in groups as an opportunist in environments from hardgrounds to soft mud, even if depleted in oxygen. It probably dispersed via larvae.