The bivalve Aulacomyella from the Early Tithonian (Late Jurassic) of Antarctica

Abstract

The bivalve Aulacomyella is described formally from Tithonian deposits of the Antarctic Peninsula region for the first time. Two species are recognized. A. willeyi Kelly sp. nov. was collected in situ from the Nordenskjöld Formation, Longing Gap on the east coast of Graham Land, and in clasts reworked into Cretaceous glide block deposits on James Ross Island. A. cf. problematica Furlani is recorded from the Himalia Ridge Formation, Fossil Bluff Group, Alexander Island. These Antarctic records are the first published systematic descriptions of the genus from the Southern Hemisphere. Together with Mexican and Turkish records, they represent the last known occurrences of this genus. Globally the genus is particularly abundant during the Kimmeridgian and Early Tithonian stages and is therefore of value as a biostratigraphic indicator. It was almost certainly an epibyssate suspension feeder, although the precise palaeoecological setting for Aulacomyella is uncertain. It normally occurs in black shales or mudstones. The most likely life habits were either living epifaunally on the sea floor, where it bloomed under episodic dysaerobic conditions in an otherwise anaerobic environment, or pseudoplanktonically infesting floating sea weeds etc. Of these hypotheses the former is preferred here.