Cefalópodos del Ordovícico Medio de la Formación Valongo, norte de Portugal

Abstract

Ordovician cephalopods from the Valongo Formation are among the first Ordovician fossils described from the Iberian Peninsula. The present review shows a lower taxonomical diversity than previously reported. Large endocerids and orthocerids are abundant in beds of early Oretanian (Middle Darriwilian) age, and orthocerids and some tarphycerids occur in strata of early Dobrotivian (Late Darriwilian) age. Despite the poor preservation in shales and the absence of internal structures, five different forms of longicones were identified, remaining them in open nomenclature. Tarphycerids are better recognizable and belong to the late Darriwilian forms Trocholites fugax and T. cf. depressus, with the former species recorded over a wide area of Ibero-Armorica and Bohemia, and the second related to a Baltic form. The occurrence of the genus Trocholites among Circumpolar Gondwana cephalopod faunas is consistent with the sporadic transfer of warm to temperate water masses southwards from the vicinity of Baltica, through a period of climatic disturbances affecting the southern hemisphere during the late Darriwilian.