The oldest known cyclophoroidean land snails (Caenogastropoda) from Asia

The earliest Miocene (Aquitanian, 23–21 Ma) Hang Mon Formation at Hang Mon in Northern Vietnam has yielded a rich assemblage of terrestrial gastropods. Four species from this assemblage belong to the land caenogastropod superfamily Cyclophoroidea. Three of these are assigned to genera with Recent representatives in Southeast Asia and are described as new species: Cyclophorus hangmonensis Raheem & Schneider sp. nov. (Cyclophoridae: Cyclophorini), Alycaeus sonlaensis Raheem & Schneider sp. nov. (Cyclophoridae: Alycaeinae) and Tortulosa naggsi Raheem & Schneider sp. nov (Pupinidae: Pupinellinae). These fossil species represent the earliest records for their genera and are thus of great value for calibrating molecular phylogenies of the Cyclophoroidea. The fourth species is represented only by poorly preserved fragments and is retained in open nomenclature in the Cyclophoridae. While extant Cyclophoroidea have their greatest diversity in Tropical Asia, the oldest fossils described to date from the region are from the Late Pleistocene. The fossils from Hang Mon predate these by more than 20 million years and are also globally among the earliest cyclophoroideans recorded from the area of the present-day forested Tropics. Cyclophoroidea older than the Miocene are only known from Europe. Given that Recent Cyclophoridae and Pupinidae are typically associated with tropical forests, it seems likely that the Hang Mon fossils were also tropical forest taxa and that suitable habitat was present in the general vicinity of Hang Mon in the earliest Miocene.