Department of Biology, Baylor University, Waco, Texas, USA.
Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, USA.
J Anat. 2022 Feb;240(2):226-252. doi: 10.1111/joa.13557. Epub 2021 Oct 26.
Secondarily aquatic tetrapods have many unique morphologic adaptations for life underwater compared with their terrestrial counterparts. A key innovation during the land-to-water transition was feeding. Pinnipeds, a clade of air-breathing marine carnivorans that include seals, sea lions, and walruses, have evolved multiple strategies for aquatic feeding (e.g., biting, suction feeding). Numerous studies have examined the pinniped skull and dental specializations for underwater feeding. However, data on the pinniped craniofacial musculoskeletal system and its role in aquatic feeding are rare. Therefore, the objectives of this study were to conduct a comparative analysis of pinniped craniofacial musculature and examine the function of the craniofacial musculature in facilitating different aquatic feeding strategies. We performed anatomic dissections of 35 specimens across six pinniped species. We describe 32 pinniped craniofacial muscles-including facial expression, mastication, tongue, hyoid, and soft palate muscles. Pinnipeds broadly conform to mammalian patterns of craniofacial muscle morphology. Pinnipeds also exhibit unique musculoskeletal morphologies-in muscle position, attachments, and size-that likely represent adaptations for different aquatic feeding strategies. Suction feeding specialists (bearded and northern elephant seals) have a significantly larger masseter than biters. Further, northern elephant seals have large and unique tongue and hyoid muscle morphologies compared with other pinniped species. These morphologic changes likely help generate and withstand suction pressures necessary for drawing water and prey into the mouth. In contrast, biting taxa (California sea lions, harbor, ringed, and Weddell seals) do not exhibit consistent craniofacial musculoskeletal adaptations that differentiate them from suction feeders. Generally, we discover that all pinnipeds have well-developed and robust craniofacial musculature. Pinniped head musculature plays an important role in facilitating different aquatic feeding strategies. Together with behavioral and kinematic studies, our data suggest that pinnipeds' robust facial morphology allows animals to switch feeding strategies depending on the environmental context-a critical skill in a heterogeneous and rapidly changing underwater habitat.
与它们的陆地同类相比，二次水生四足动物有许多独特的形态适应水下生活。在从陆地到水域的过渡过程中，一个关键的创新是进食。鳍足类动物是一类呼吸空气的海洋食肉动物，包括海豹、海狮和海象，它们已经进化出了多种水生进食策略（例如，咬、吸吮进食）。许多研究都研究了鳍足类动物的头骨和牙齿特化结构，以适应水下进食。然而，关于鳍足类动物的颅面骨骼肌肉系统及其在水生进食中的作用的数据却很少。因此，本研究的目的是对鳍足类动物的颅面肌肉进行比较分析，并研究颅面肌肉在促进不同水生进食策略中的作用。我们对六个鳍足类物种的 35 个标本进行了解剖学解剖。我们描述了 32 种鳍足类颅面肌肉，包括面部表情、咀嚼、舌头、舌骨和软腭肌肉。鳍足类动物广泛符合哺乳动物的颅面肌肉形态模式。鳍足类动物还表现出独特的骨骼肌肉形态，包括肌肉位置、附着点和大小，这可能代表了对不同水生进食策略的适应。吸吮进食专家（胡须海豹和北方象海豹）的咬肌比咬人者大得多。此外，与其他鳍足类物种相比，北方象海豹的舌头和舌骨肌肉形态较大且独特。这些形态变化可能有助于产生和承受将水和猎物吸入口腔所需的吸力。相比之下，咬人者（加利福尼亚海狮、港湾、环斑和威德尔海豹）并没有表现出与吸吮者不同的颅面骨骼肌肉适应性。一般来说，我们发现所有的鳍足类动物都有发达而强壮的颅面肌肉。鳍足类动物的头部肌肉在促进不同的水生进食策略中起着重要作用。结合行为和运动学研究，我们的数据表明，鳍足类动物强壮的面部形态使动物能够根据环境背景切换进食策略——这是在异质和快速变化的水下栖息地中生存的一项关键技能。
