A cephalopod fauna from the middle Ordovician of Saudi Arabia

A small collection of cephalopods from the middle Ordovician of the Tabuk r egion of Saudi Arabia consists entirely of orthoconic longicones tentativel y referred to the actinocerid genus Mesaktoceras? and pseudorthocerid Sacto ceras?. Both taxa have Australasian affinities. Circumpolar Gondwana cephal opod faunas in the mid Ordovician were of low diversity and dominated by or thocerids, whilst actinocerids were largely restricted to low palaeolatitud es. The presence of Mesaktoceras? and Sactoceras? in a benthonic fauna belo nging to the Neseuretus community is regarded as anomalous. Comparison is m ade with the occurrence of Trocholites in middle Ordovician Iberian success ions. It has been suggested that Trocholites may have arrived in the Iberia n area from Baltica through the transfer of bodies of warm water in storm m asses. Mesaktoceras? and Sactoceras? may have arrived (albeit temporarily) in Saudi Arabia from Australasia through a similar process.