Late Valanginian (Early Cretaceous) lamellaptychi of the genus Mortilletilamellaptychus were collected from seven ammonite-controlled sections in south-eastern France demonstrate distinct changes in ribbing during growth. Simpler juvenile ribbing, which is essentially uniform for all of the specimens studied, differs distinctly from the complicated arrangement of the adult ribs. Changes in ribbing morphology were observed in the five species studied, two of which were identified as new (i.e. Mortilletilamellaptychus heterocostatus sp. nov. and M. bicostatus sp. nov.).
Late Berriasian–earliest Valanginian lamellaptychi (Cephalopoda) are described in detail for the first time. With one exception, all species belong to early representatives of Mortilletilamellaptychus. The majority of the well dated aptychi come from the cephalopod-rich sediments of the Vocontian Basin in south-eastern France; others are from south-eastern Spain. Thorolamellaptychus anglesensis sp. nov. is introduced.
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