Record of Juraphyllites ex gr. libertus (Gemmellaro 1884) from the Ururoan Stage (Early Jurassic, New Zealand) and observations on the paleoenvironmental dynamics of the Ururoan ammonite fauna

Abstract

Juraphyllites libertus is a common member of Tethyan Juraphyllitid assemblages of Pliensbachian age in Central and Southern Europe and the eastern Mediterranean. Judging from these occurrences, the age of J. ex gr. libertus in New Zealand probably ranges from the Jamesoni Zone to the Margaritatus Zone, i.e. from the lowermost zone of the Lower Pliensbachian to the middle zone of the Upper Pliensbachian. The presence in New Zealand of J. ex gr. libertus, together with other ammonite taxa previously recorded from the Ururoan (Harpoceras, Zugodactylites and Catacoeloceras), all with strong Tethyan affinities, is discussed. The paleoenvironmental factors that enabled them to migrate to the southwest Pacific, on the southern margin of Gondwana are considered. Their migration was probably facilitated by a combination of the following factors: 1. dispersal ability of taxa; 2. global sea levels; 3. availability of migration routes; 4. local seawater temperatures; and 5. local facies conditions.