On the Middle Jurassic - Early Cretaceous Megatrigoniinae (Bivalvia, Trigoniida): their biogeography, evolution and classification

Megatrigoniine bivalves are the rootstock of a major trigoniid radiation in the Late Jurassic and Early Cretaceous. They appeared first in the Middle Bajocian of the Andean Province and are predominantly Gondwanic in distribution. Their centre of radiation and dispersal was the Andean Province, from where they spread into the American Province in the Callovian and reached the Ethiopian Province in the Late Tithonian. They became extinct in the Gondwanic Realm in the early Late Albian. Far from being cosmopolitan, megatrigoniine bivalves are highly provincial and restricted to the Cordilleran, American, Andean and Ethiopian provinces. Current interpretation of the subfamily is reviewed, 36 species and subspecies are analyzed and assigned to 10 genera, 4 of which are new: Californigonia, Craginella, Damborenella, and Bengtsonella.