Fuchs Dirk, Hoffmann René, Klug Christian
Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Straße 10, 80333 Munich, Germany.
Institute of Geology, Mineralogy, & Geophysics, Ruhr-Universität Bochum, 44801 Bochum, Germany.
Swiss J Palaeontol. 2021;140(1):27. doi: 10.1186/s13358-021-00241-z. Epub 2021 Dec 20.
The cephalopod arm armature is certainly one of the most important morphological innovations responsible for the evolutionary success of the Cephalopoda. New palaeontological discoveries in the recent past afford to review and reassess origin and homology of suckers, sucker rings, hooks, and cirri. Since a priori character state reconstructions are still ambiguous, we suggest and discuss three different evolutionary scenarios. Each of them is based on the following assumptions: (1) Neocoleoidea uniting extant Decabrachia and Octobrachia is monophyletic (= proostracum-bearing coleoids); (2) extinct Belemnitida and Diplobelida are stem decabrachians; (3) proostracum-less coleoids (Hematitida, Donovaniconida, Aulacoceratida) represent stem-neocoleoids; (4) Ammonoidea and Bactritoidea are stem coleoids. We consider a scenario where belemnoid hooks derived from primitive suckers as well-supported. Regarding belemnoid hooks and suckers as homologues implies that belemnoid, oegopsid, and probably ammonoid arm hooks arose through parallel evolution. Our conclusions challenge the widespread opinion, whereupon belemnoid hooks evolved de novo, and instead support earlier ideas formulated by Sigurd von Boletzky.
头足类动物的腕部结构无疑是对头足纲动物进化成功起到重要作用的形态学创新之一。近期新的古生物学发现使得我们能够重新审视和评估吸盘、吸盘环、钩和触须的起源及同源性。由于先验特征状态重建仍然不明确，我们提出并讨论了三种不同的进化场景。每一种场景都基于以下假设：（1）将现存的十腕总目和八腕总目联合起来的新鞘亚纲是单系的（=有前甲的鞘亚纲）；（2）已灭绝的箭石目和双箭石目是十腕总目的干群；（3）无前甲的鞘亚纲（血箭石目、多诺万石目、管角石目）代表新鞘亚纲的干群；（4）菊石亚纲和杆石亚纲是鞘亚纲的干群。我们认为一种箭石类钩源自原始吸盘的场景是有充分依据的。将箭石类钩和吸盘视为同源意味着箭石类、开眼亚目的以及可能菊石类的腕钩是通过平行进化产生的。我们的结论挑战了箭石类钩是重新演化而来的这一广泛观点，转而支持西格德·冯·博莱茨基之前提出的观点。
