Sphenothallus is a problematic extinct genus lately attributed to the conulariids.

It was widespread in shallow marine environments during the Paleozoic.

[2][4] Sphenothallus is represented in the Cambrian period in the Kaili biota and the Mount Stephen trilobite beds, where it co-occurs with the similar organisms Cambrorhythium and Byronia.

[1] It is known in younger strata in Canada and the US, surviving at least until the Mississippian.

[3] Sphenothallus lived in groups as an opportunist in environments from hardgrounds to soft mud, even if depleted in oxygen.