Late Ordovician cephalopods from Morocco and their implications

Abstract The present paper describes the latest cephalopod fauna from the Upper Ordovician in the Anti-Atlas region, Morocco. Two species are reported herein belonging to two genera including one new species, Tafadnatoceras elfechtense sp. nov. and Isorthoceras sp.; the latter of which marks the first occurrence of the genus in Morocco. The discovery extends the distribution of late Katian cephalopod faunas globally, correlative with other high-latitude cephalopod faunas such as those from the Zagros region of Iran. After the evolutionary peak of the Great Ordovician Biodiversification Event in the Middle to early Late Ordovician, a marine ecosystem crisis led to a decline in biodiversity afterwards. Although the cephalopods continued to flourish in low-latitude regions, the palaeogeographic differentiation was observed in the Anti-Atlas region, where the faunas in the high-latitude region experienced a significant decline. The pattern aligns with the changes in the latitudinal diversity gradient from the Middle to Late Ordovician. Furthermore, the distributions of the cephalopod faunas in the Late Ordovician may have been influenced by the emergence of the high-latitude cold current.