New species of Franchia and Protozigzagiceras (Ammonoidea, Middle Jurassic): the phyletic origin of Zigzagiceratinae

Three genera and seven species belonging to the subfamily Zigzagiceratinae (family Perisphinctidae) are described from the Lower Bathonian of France and Saudi Arabia. Intraspecific dimorphism is recognized. A revision of the genus Franchia proposed by Sturani (1967), based on the syntypes and new specimens from south-east France, is presented. Franchia arkelli Sturani, Franchia subalpina sp. nov., Protozigzagiceras torrensi (Sturani), Protozigzagiceras tethycum sp. nov., Protozigzagiceras flexum sp. nov. and Protozigzagiceras densum sp. nov. are described from the Digne–Castellane region of south-east France. Megazigzagiceras subarabicum, gen. et sp. nov. is described from the Dharma region of Saudi Arabia. The successive Early Bathonian species of Franchia and Protozigzagiceras herein identified in West Tethyan areas, as members of the Mediterranean–Caucasian Subrealm, formed lasting separate peramorphoclines characterized by increasing hydrodynamic coiling of the shell. In contrast, r...