berkutensis from the Malyi Karatau, Kazakhstan (both Lower Tremadocian), are both very poorly known and it remains uncertain to which family they could best be assigned.

The first certain Illaenid is I. hinomotoensis from the Upper Tremadocian of North China and South Korea.

The earliest species known from Laurentia (western Ireland) is I. weaveri, probably latest Floian.

These early occurrences are from the tropics, but during the Darriwilian the family spread over southern Gondwana, and became cosmopolitan for the remainder of the Ordovician, although most genera had limited distributions.

The genus Stenopareia survived the Ordovician–Silurian extinction events and the family slightly rebounded with 26 species divided over three genera during the Silurian.