First Middle–Late Jurassic gladius vestiges provide new evidence on the detailed origin of incirrate and cirrate octopuses (Coleoidea)

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First Middle–Late Jurassic gladius vestiges provide new evidence onthedetailed origin ofincirrate andcirrate octopuses (Coleoidea) Dirk Fuchs, Gunter Schweigert 2017 (PDF via Springer shared by author)

Abstract
Limpet-like and nonmineralized fossils from the upper Kimmeridgian Nusplingen Plattenkalk are identified as internal shells of coleoid cephalopods, more specifically as octobrachian gladii. The significantly reduced median field provokes us to consider this new gladius type to be shorter than the mantle length. It is consequently seen as a vestigial gladius. The first recognition of an unpaired gladius vestige in the fossil record sheds new light on the evolutionary history of the gladius vestiges of incirrate and cirrate Octopoda. Patelloctopus ilgi sp. nov. is most similar to Callovian Pearceiteuthis buyi in having a rudimentary median field with an extraordinary large opening angle and radiating ribs on the lateral fields. Both P. ilgi sp. nov. and P. buyi are therefore combined in the new family Patelloctopodidae. The patella-shaped lateral fields of the gladius vestige exposes Patelloctopus and Pearceiteuthis as members of the superfamily Muensterelloidea, which includes, apart from Patelloctopodidae, the Muensterellidae and Enchoteuthidae. The unpaired patelloctopodid gladius vestige is morphologically intermediate between the muensterelloid gladius type and the paired (bipartite) gladius vestige of Late
Cretaceous Palaeoctopodidae (Palaeoctopus, Keuppia). The gladius vestige morphology suggests that the mode of locomotion and the life style of these shallow water inhabitants were similar to those of extant deep-sea octopods (Cirrata) and that the Patelloctopodidae represents the stem group of the Octopoda (Cirrata and Incirrata), although Patelloctopus ilgi sp. nov. might alternatively be a stem incirrate.
 

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