Zugodactylites

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Zugodactylites is an extinct genus of ammonite cephalopods from the early Toarcian stage of the Lower Jurassic (Fibulatum zone). Fossils have been found in Europe, Russia, and Canada. The shells are compressed in cross-section, and can be equidimensional or slightly depressed. Before reaching the adult opening, the shell shows a collar and a constriction. The ribs are dense and often bifurcate at sharp ventrolateral tubercles or spines; fibulate ribs are absent. There is sexual dimorphism, with Gabillytes representing microconchs (the smaller sex). Zugodactylites evolved from Peronoceras. The type species is Ammonites braunianus (d’Orbigny, 1845). Synonyms include Omolonoceras and Gabillytes.