Proharpoceras Chao: a new ammonoid lineage surviving the end-Permian mass extinction
Résumé
Based on new, bed-rock controlled material from northwestern Guangxi and Oman, the Early Triassic genus Proharpoceras Chao is shown to be a representative of Otocerataceae. Character analysis excludes a direct link with the Griesbachian Otoceratidae and favours a derivation of Proharpoceras from the late Permian Anderssonoceratidae. The biostratigraphic range of Proharpoceras is restricted to the Smithian and its biogeographic distribution comprises Oman, South China, and Primorye, thus indicating an essentially low palaeolatitudinal distribution. Proharpoceras has no apparent relatives among other Early and Middle Triassic Ceratitida and is thus considered to be the last representative of Otocerataceae. This offshoot of the late Permian Anderssonoceratidae implies that an additional ammonoid lineage survived the end Permian extinction and that it dwindled away for some 2 Myr before going extinct.