Two Mississippian Caenogastropod limpets from Australia and their meaning for the ancestry of the Caenogastropoda

Abstract

Two new limpets with a caenogastropod-type larval shell are described from the Mississippian (Early Carboniferous) of Australia and assigned to Australoscutula n. gen. of the family Pragoscutulidae. This family has previously been reported only from the Early Devonian of Europe (Czech Republic, Prague Basin). Therefore, it survived the Late Devonian biotic crisis. the fact that one of the earliest certain caenogastropods has a patelliform shell is noteworthy given most other Middle to Late Paleozoic caenogastropods are high-spired or fusiform. Pragosutulidae are interpreted as an early patelliform caenogastropod offshoot derived from coiled ancestors. the Pragoscutulidae are the oldest gastropod limpets with well-preserved larval shells. Their teleoconch is entirely limpet-shaped without helicoid coiling. However, the helicoid turbiniform larval shells suggests that this group evolved from an ancestor with turbiniform or even high-spired adult shell. Moreover, the multi-whorled dextral larval shells show that Pragoscutulidae are Caenogastropoda and document that early Caenogastropoda displayed considerable disparity.