Krahl Anna, Werneburg Ingmar
Paläontologische Sammlung, Fachbereich Geowissenschaften der Universität Tübingen, Tübingen, Germany.
Senckenberg Center for Human Evolution and Palaeoenvironment an der Universität Tübingen, Tübingen, Germany.
Anat Rec (Hoboken). 2023 Jun;306(6):1323-1355. doi: 10.1002/ar.25119. Epub 2022 Dec 2.
The diapsid plesiosaurs were pelagic and inhabited the oceans from the Triassic to the Cretaceous. A key evolutionary character of plesiosaurs is the four wing-like flippers. While it is mostly accepted that plesiosaurs were underwater fliers like marine turtles, penguins, and maybe whales, other swimming styles have been suggested in the past. These are rowing and a combination of rowing and underwater flight (e.g., pig-nosed turtle, sea lion). Underwater fliers use lift in contrast to rowers that employ drag. For efficiently profiting of lift during underwater flying, it is necessary that plesiosaurs twisted their flippers by muscular activity. To research the evolution of flipper twisting in plesiosaurs and functionally analogous taxa, including turtles, we used anatomical network analysis (AnNA) and reassessed distal flipper muscle functions. We coded bone-to-bone and additionally muscle-to-bone contacts in N × N matrices for foreflippers of the plesiosaur, the loggerhead sea turtle, the pig-nosed turtle, the African penguin, the California sea lion, and the humpback whale based on literature data. In "R," "igraph" was run by using a walktrap algorithm to obtain morphofunctional modules. AnNA revealed that muscle-to-bone contacts are needed to detect contributions of modules to flipper motions, whereas only-bone matrices are not informative for that. Furthermore, the plesiosaur, the marine turtles, the seal, and the penguin flipper twisting mechanisms, but the penguin cannot actively twist the flipper trailing edge. Finally, the foreflipper of the pig-nosed turtle and of the whale is not actively twisted during swimming.
双孔类鳍龙是远洋生物,从三叠纪到白垩纪都栖息在海洋中。鳍龙的一个关键进化特征是四个像翅膀一样的鳍状肢。虽然大多数人认为鳍龙像海龟、企鹅,也许还有鲸鱼一样是水下飞行者,但过去也有人提出了其他游泳方式。这些方式是划水以及划水和水下飞行的组合(例如猪鼻龟、海狮)。水下飞行者利用升力,而划水者则利用阻力。为了在水下飞行时有效地利用升力,鳍龙有必要通过肌肉活动扭转它们的鳍状肢。为了研究鳍龙以及包括海龟在内的功能类似类群中鳍状肢扭转的进化,我们使用了解剖网络分析(AnNA)并重新评估了鳍状肢远端肌肉的功能。我们根据文献数据,将鳍龙、蠵龟、猪鼻龟、非洲企鹅、加利福尼亚海狮和座头鲸前肢的骨与骨以及肌肉与骨的接触情况编码到N×N矩阵中。在“R”语言中,使用walktrap算法运行“igraph”来获得形态功能模块。AnNA表明,需要肌肉与骨的接触来检测模块对鳍状肢运动的贡献,而仅骨矩阵对此并无信息价值。此外,鳍龙、海龟、海豹和企鹅具有鳍状肢扭转机制,但企鹅无法主动扭转鳍状肢后缘。最后,猪鼻龟和鲸鱼的前肢在游泳时不会主动扭转。