Key innovations in Mesozoic ammonoids: the multicuspidate radula and the calcified aptychus

摘要: A nearly complete radula with seven elements per row preserved inside of an isolated, bivalved, calcitic lower jaw (= aptychus) the Late Jurassic ammonite Aspidoceras is described from Fossillagerstatte Painten (Bavaria, southern Germany). It largest known and first record for Perisphinctoidea. The multicuspidate tooth (ctenodont type radula) present short cusps. Owing to significant morphological differences between aptychophoran ammonoid radulae, their possible function discussed, partly in comparison modern cephalopod gastropod radulae. Analogies evolution pharyngeal jaws cichlid fishes buccal apparatus raise possibility that a allowed functional decoupling jaw. radula, therefore, represents key innovation which calcified Cretaceous ammonites. Possible triggers this change during early Toarcian are discussed. Finally, we hypothesize potential adaptations ammonoids different feeding niches based on radular morphologies.