A cephalopod fauna from the middle Ordovician of Saudi Arabia

Abstract

A small collection of cephalopods from the middle Ordovician of the Tabuk region of Saudi Arabia consists entirely of orthoconic longicones tentatively referred to the actinocerid genus Mesaktoceras? and pseudorthocerid Sactoceras?. Both taxa have Australasian affinities. Circumpolar Gondwana cephalopod faunas in the mid Ordovician were of low diversity and dominated by orthocerids, whilst actinocerids were largely restricted to low palaeolatitudes. The presence of Mesaktoceras? and Sactoceras? in a benthonic fauna belonging to the Neseuretus community is regarded as anomalous. Comparison is made with the occurrence of Trocholites in middle Ordovician Iberian successions. It has been suggested that Trocholites may have arrived in the Iberian area from Baltica through the transfer of bodies of warm water in storm masses. Mesaktoceras? and Sactoceras? may have arrived (albeit temporarily) in Saudi Arabia from Australasia through a similar process.