A redescription of the endemic antiarch placoderm Asterolepis thule from the Middle Devonian (Givetian) of Shetland and its biostratigraphical horizon

Abstract

The Givetian (Middle Devonian) antiarch Asterolepis thule was first described in 1932 and its stratigraphical horizon was poorly understood as were all the Devonian deposits in the SE of Shetland (South East Shetland Group). Since that time a greater understanding of the age of these deposits has been made. This, coupled with the greater clarity of the biostratigraphy of the Devonian of Scotland and its correlation with the Baltic Devonian, has allowed the species to be placed in a biostratigraphical zonation. The species is confined to Sumburgh Head and so appears endemic. Other species are also endemic and there are some relict fauna in the South East Shetland Group. This suggests that the South East Shetland Group fauna originated mostly in isolation to the main depositional areas of the Givetian in Scotland and elsewhere, although some species are more cosmopolitan.